Method for the production of liquefied natural gas

ABSTRACT

A system and method for producing liquefied natural gas are provided. The method may include compressing a process stream containing natural gas in a compression assembly to produce a compressed process stream. The method may also include removing non-hydrocarbons from the compressed process stream in a separator, and cooling the compressed process stream with a cooling assembly to thereby produce a cooled, compressed process stream containing natural gas in a supercritical state. The method may further include expanding a first portion and a second portion of the natural gas from the cooled, compressed process stream in a first expansion element and a second expansion element to generate a first refrigeration stream and a second refrigeration stream, respectively. The method may further include cooling the natural gas in the cooled, compressed process stream to a supercritical state with the first and second refrigeration streams to thereby produce the liquefied natural gas.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of co-pending U.S. patentapplication Ser. No. 14/566,119, filed on Dec. 10, 2014, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/932,668,filed on Jan. 28, 2014. The aforementioned patent applications arehereby incorporated by reference in their entirety into the presentapplication to the extent consistent with the present application.

BACKGROUND

The combustion of conventional fuels, such as gasoline and diesel, hasproven to be essential in a myriad of industrial processes. Thecombustion of gasoline and diesel, however, may often be accompanied byvarious drawbacks including increased production costs and increasedcarbon emissions. In view of the foregoing, recent efforts have focusedon alternative fuels with decreased carbon emissions, such as naturalgas, to combat the drawbacks of combusting conventional fuels. Inaddition to providing a “cleaner” alternative fuel with decreased carbonemissions, combusting natural gas may also be relatively safer thancombusting conventional fuels. For example, the relatively low densityof natural gas allows it to safely and readily dissipate to theatmosphere in the event of a leak. In contrast, conventional fuels(e.g., gasoline and diesel) with a relatively high density tend tosettle or accumulate in the event of a leak, which may present ahazardous and/or fatal working environment for nearby operators.

While the utilization of natural gas may address some of the drawbacksassociated with conventional fuels, the storage and transport of naturalgas in sufficient quantities may prevent it from being viewed as aviable alternative to conventional fuels. For example, the storageand/or transport of natural gas in appreciable quantities may becost-prohibitive and/or impracticable due to its relatively low density.Accordingly, natural gas is routinely converted into liquefied naturalgas (LNG) at an LNG plant and transported from the LNG plant to the enduser or customer by tanker trucks. The availability of LNG, however, mayoften be limited by the proximity of the customer to the LNG plant. Forexample, customers that are remotely located from the LNG plant mayoften rely on deliveries from the tanker trucks, which increase the costof utilizing LNG. Additionally, remotely located customers may often berequired to maintain larger, cost-prohibitive storage tanks to reducethe frequency of the deliveries and/or their dependence on the tankertrucks. In lieu of LNG, remotely located customers may opt to utilizelocal natural gas pipelines to produce compressed natural gas (CNG)on-site. CNG, similar to natural gas, has a lower relative density thanLNG; and thus, the storage of CNG in appreciable quantities may also becost-prohibitive and/or impracticable.

What is needed, then, is a system and method for producing LNG fromnatural gas pipelines and stranded wells.

SUMMARY

Embodiments of the disclosure may provide a method for producingliquefied natural gas. The method may include compressing a processstream containing natural gas from a natural gas source to produce acompressed process stream. The process stream may be compressed toprovide the compressed process stream in a compression assembly fluidlycoupled with the natural gas source. The method may also includeremoving one or more non-hydrocarbons from the compressed process streamin a separator fluidly coupled with the compression assembly. The methodmay further include cooling the compressed process stream with a coolingassembly fluidly coupled with the compression assembly to therebyproduce a cooled, compressed process stream containing the natural gasin a supercritical state. The method may also include expanding a firstportion of the natural gas in the cooled, compressed process stream in afirst expansion element to generate a first refrigeration stream, andexpanding a second portion of the natural gas in the cooled, compressedprocess stream in a second expansion element to generate a secondrefrigeration stream. The method may also include cooling at least aportion of the natural gas in the cooled, compressed process stream to asubcritical state with the first refrigeration stream and the secondrefrigeration stream to thereby produce the liquefied natural gas.

Embodiments of the disclosure may further provide another method forproducing liquefied natural gas. The method may include compressingnatural gas from a natural gas source in a compression assembly fluidlycoupled with the natural gas source. The method may also includeremoving water and carbon dioxide from the natural gas in a separatorfluidly coupled with the compression assembly. The method may furtherinclude cooling the natural gas to supercritical natural gas with amechanical chiller configured to receive and be driven by electricalenergy. The method may also include expanding a first portion of thesupercritical natural gas in a first expansion element to generate afirst refrigeration stream, and expanding a second portion of thesupercritical natural gas in a second expansion element to generate asecond refrigeration stream. The method may further include cooling theremaining supercritical natural gas to subcritical natural gas with thefirst refrigeration stream and the second refrigeration stream tothereby produce the liquefied natural gas.

Embodiments of the disclosure may further provide a system for producingliquefied natural gas. The system may include a compressor fluidlycoupled with a natural gas source. The compressor may be configured tocompress a process stream containing natural gas from the natural gassource to a compressed process stream. A separator may be fluidlycoupled with the compressor and configured to receive the compressedprocess stream and at least partially separate water and carbon dioxidefrom the natural gas in the compressed process stream. The system mayalso include a mechanical chiller in thermal communication with thecompressor. The mechanical chiller may be configured to cool the naturalgas in the compressed process stream to supercritical natural gas. Aturbo-expander may be fluidly coupled with the compressor and configuredto expand a first portion of the supercritical natural gas to generate afirst refrigeration stream. An expansion valve may be fluidly coupledwith the compressor and configured to expand a second portion of thesupercritical natural gas to generate a second refrigeration stream. Thesystem may further include a first heat exchanger fluidly coupled withthe turbo-expander, and a second heat exchanger fluidly coupled with theexpansion valve. The first heat exchanger may be configured to cool thesupercritical natural gas with the first refrigeration stream, and thesecond heat exchanger may be configured to cool the supercriticalnatural gas with the second refrigeration stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying Figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a process flow diagram of an exemplary system forproducing liquefied natural gas (LNG) from a natural gas source,according to one or more embodiments disclosed.

FIG. 2 illustrates a flowchart of a method for producing liquefiednatural gas, according to one or more embodiments disclosed.

FIG. 3 illustrates a flowchart of another method for producing liquefiednatural gas, according to one or more embodiments disclosed.

DETAILED DESCRIPTION

It is to be understood that the following disclosure describes severalexemplary embodiments for implementing different features, structures,or functions of the invention. Exemplary embodiments of components,arrangements, and configurations are described below to simplify thepresent disclosure; however, these exemplary embodiments are providedmerely as examples and are not intended to limit the scope of theinvention. Additionally, the present disclosure may repeat referencenumerals and/or letters in the various exemplary embodiments and acrossthe Figures provided herein. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various exemplary embodiments and/or configurationsdiscussed in the various Figures. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact.Finally, the exemplary embodiments presented below may be combined inany combination of ways, i.e., any element from one exemplary embodimentmay be used in any other exemplary embodiment, without departing fromthe scope of the disclosure.

Additionally, certain terms are used throughout the followingdescription and claims to refer to particular components. As one skilledin the art will appreciate, various entities may refer to the samecomponent by different names, and as such, the naming convention for theelements described herein is not intended to limit the scope of theinvention, unless otherwise specifically defined herein. Further, thenaming convention used herein is not intended to distinguish betweencomponents that differ in name but not function. Further, in thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to.” All numericalvalues in this disclosure may be exact or approximate values unlessotherwise specifically stated. Accordingly, various embodiments of thedisclosure may deviate from the numbers, values, and ranges disclosedherein without departing from the intended scope. Furthermore, as it isused in the claims or specification, the term “or” is intended toencompass both exclusive and inclusive cases, i.e., “A or B” is intendedto be synonymous with “at least one of A and B,” unless otherwiseexpressly specified herein.

FIG. 1 illustrates a process flow diagram of an exemplary system 100 forproducing compressed natural gas (CNG) and/or liquefied natural gas(LNG) from a natural gas source 102, according to one or moreembodiments. In least one embodiment, the system 100 may include acompression assembly 104, a cooling assembly 106, and a liquefactionassembly 108 coupled with and/or in thermal communication with oneanother. The system 100 may be configured to circulate a process streamcontaining natural gas from the natural gas source 102 to one or moreportions or assemblies thereof. For example, the system 100 may befluidly coupled with the natural gas source 102 via line 202 andconfigured to circulate the process stream containing the natural gasfrom the natural gas source 102 to the compression assembly 104, thecooling assembly 106, and/or the liquefaction assembly 108.

In one or more portions or assemblies of the system 100, the natural gasin the process stream may be in a liquid phase, a gaseous phase, a fluidphase, a subcritical state, a supercritical state, or any other phasesor states, or any combination thereof. For example, as further describedherein, the compression assembly 104 and the cooling assembly 106 may atleast partially compress and cool the natural gas in the process streamfrom the gaseous phase to the supercritical state (e.g., CNG). Inanother example, as further described herein, the liquefaction assembly108 may further cool the natural gas in the process stream from thesupercritical state (e.g., CNG) to the subcritical state (e.g., LNG).

In at least one embodiment, the natural gas source 102 may be or includea natural gas pipeline, a stranded natural gas wellhead, or the like, orany combination thereof. For example, the natural gas source 102 may below-pressure natural gas pipeline. The natural gas from the natural gassource 102 may include one or more hydrocarbons. For example, thenatural gas may include methane, ethane, propane, butanes, pentanes, orthe like, or any combination thereof. In at least one embodiment,methane may be a major component of the natural gas. For example, theconcentration of methane in the natural gas from the natural gas source102 may be greater than about 80%, greater than about 85%, greater thanabout 90%, or greater than about 95%. In at least one embodiment, thenatural gas from the natural gas source 102 may be or include a mixtureof one or more hydrocarbons (e.g., methane) and one or morenon-hydrocarbons. Illustrative non-hydrocarbons may include, but are notlimited to, water, carbon dioxide (CO₂), hydrogen sulfide, helium,nitrogen, or the like, or any combination thereof.

In at least one embodiment, the compression assembly 104 may include oneor more compressors (one is shown 112) fluidly coupled with the naturalgas source 102 and configured to compress and/or pressurize the naturalgas from the natural gas source 102. For example, as illustrated in FIG.1, the compressor 112 may be fluidly coupled with the natural gas source102 via lines 202, 206, and 208. Illustrative compressors 112 mayinclude, but are not limited to, supersonic compressors, centrifugalcompressors, axial flow compressors, reciprocating compressors, rotatingscrew compressors, rotary vane compressors, scroll compressors,diaphragm compressors, or the like, or any combination thereof. In atleast one embodiment, the compressor 112 may include one or morecompressor stages (four are shown 114, 116, 118, 120). For example, asillustrated in FIG. 1, the compressor 112 may include a first compressorstage 114, a second compressor stage 116, a third compressor stage 118,and a fourth compressor stage 120 coupled with one another via adriveshaft 122 of the compressor 112.

In at least one embodiment, the compression assembly 104 may include oneor more drivers or motors (one is shown 124) coupled with and configuredto drive the compressor 112 and/or one or more components thereof. Forexample, as illustrated in FIG. 1, the driver 124 may be coupled withand configured to drive the compressor stages 114, 116, 118, 120 of thecompressor 112 via the driveshaft 122. Illustrative drivers 124 mayinclude, but are not limited to, electric motors, turbines, and/or anyother devices capable of driving the compressor 112 and/or thecompressor stages 114, 116, 118, 120 thereof. In an exemplaryembodiment, illustrated in FIG. 1, the driver 124 may be an electricmotor configured to receive and be driven by electrical energy.

In at least one embodiment, the system 100 may include a powergeneration system 126 configured to generate electrical energy to driveone or more components or assemblies of the system 100. For example, thepower generation system 126 may be configured to generate electricalenergy to drive the electric motor 124 of the compression assembly 104.In at least one embodiment, the power generation system 126 may includean internal combustion engine 130 and a generator 128 operably coupledwith the internal combustion engine 130. As illustrated in FIG. 1, theinternal combustion engine 130 may be fluidly coupled with the naturalgas source 102 via line 264 and configured to receive and combust atleast a portion of the natural gas from the natural gas source 102 togenerate mechanical energy. The generator 128 may be configured toconvert the mechanical energy from the internal combustion engine 130 toelectrical energy and deliver the electrical energy to the electricmotor 124 via line 266 to thereby drive the electric motor 124 and thecompressor 112.

In at least one embodiment, the compression assembly 104 may include oneor more heat exchangers or coolers (four are shown 132, 134, 136, 138)configured to absorb or remove heat from the process stream flowingtherethrough. As illustrated in FIG. 1, the coolers 132, 134, 136, 138may be fluidly coupled with the compressor stages 114, 116, 118, 120 andconfigured to remove heat generated in the compressor stages 114, 116,118, 120. For example, compressing the process stream in the compressorstages 114, 116, 118, 120 may generate heat (e.g., heat of compression)in the process stream, and the coolers 132, 134, 136, 138 may beconfigured to remove the heat of compression from the process streamand/or the natural gas contained therein.

In at least one embodiment, each of the coolers 132, 134, 136, 138 maybe fluidly coupled with and disposed downstream from the respectivecompressor stages 114, 116, 118, 120 of the compressor 112. For example,a first cooler 132 may be fluidly coupled with and disposed downstreamfrom the first compressor stage 114 via line 262, a second cooler 134may be fluidly coupled with and disposed downstream from the secondcompressor stage 116 via line 210, a third cooler 136 may be fluidlycoupled with and disposed downstream from the third compressor stage 118via line 250, and a fourth cooler 138 may be fluidly coupled with anddisposed downstream from the fourth compressor stage 120 via line 222.As illustrated in FIG. 1, the first cooler 132 may also be fluidlycoupled with lines 202 and 206 via line 204.

In at least one embodiment, a heat transfer medium may flow through thecoolers 132, 134, 136, 138 to absorb the heat in the process streamflowing therethrough. Accordingly, the heat transfer medium may have ahigher temperature when it exits the coolers 132, 134, 136, 138, and theprocess stream may have a lower temperature when it exits the coolers132, 134, 136, 138. The heat transfer medium may be or include water,steam, a refrigerant, a process gas, such as carbon dioxide, propane, ornatural gas, or the like, or any combination thereof. In an exemplaryembodiment, the heat transfer medium may be or include a refrigerantfrom the cooling assembly 106. In at least one embodiment, the heattransfer medium from the coolers 132, 134, 136, 138 may providesupplemental heating to one or more systems and/or assemblies of thesystem 100. For example, the heat transfer medium containing the heatabsorbed from the coolers 132, 134, 136, 138 may provide supplementalheating to a heat recovery unit (HRU) (not shown).

As previously discussed, the natural gas from the natural gas source 102may be or include a mixture of one or more hydrocarbons (e.g., methane,ethane, etc.) and one or more non-hydrocarbons (e.g., water, CO₂,hydrogen sulfide, etc.). In at least one embodiment, the system 100 mayinclude a separator 140 fluidly coupled with the compression assembly104 and configured to at least partially separate or remove one or moreof the non-hydrocarbons from the natural gas contained in the processstream. For example, as illustrated in FIG. 1, the separator 140 may befluidly coupled with and disposed downstream from the second compressorstage 116 and the second cooler 134 of the compression assembly 104 vialines 210 and 212. In at least one embodiment, the separator 140 may beconfigured to remove water and/or CO₂ from the natural gas in theprocess stream to increase the concentration of the hydrocarbons in theprocess stream and/or prevent the natural gas in the process stream fromsubsequently crystallizing (e.g., freezing) in one or more portionsand/or downstream processes of the system 100. For example, in one ormore portions and/or downstream processes of the system 100, the processstream may be cooled to or below a freezing point of one or more of thenon-hydrocarbons (e.g., water and/or CO₂). Accordingly, removing waterand/or CO₂ from the natural gas contained in the process stream mayprevent the subsequent crystallization of the process stream in thesystem 100.

In at least one embodiment, the separator 140 may include or contain oneor more adsorbents configured to separate the non-hydrocarbons from thenatural gas in the process stream. The adsorbents may include, but arenot limited to, one or more molecular sieves, zeolites, metal-organicframeworks, or the like, or any combination thereof. In at least oneembodiment, the adsorbent, such as the molecular sieve, may be activatedat varying temperatures and/or pressures. The adsorbent may have anadsorptive capacity determined by an amount of an adsorbate or thenon-hydrocarbons (e.g., CO₂, water, etc.) separated by the adsorbentunder predetermined conditions (e.g., temperature and/or pressure).

In at least one embodiment, the separator 140 and/or the adsorbentcontained therein may be configured to separate the non-hydrocarbonsfrom the process stream at a predetermined pressure. For example, theseparator 140 and/or the adsorbent may be configured to separate thenon-hydrocarbons (e.g., CO₂ and/or water) at a pressure from a low ofabout 600 kPa, about 650 kPa, about 700 kPa, about 750 kPa, about 800kPa, about 850 kPa, about 900 kPa, about 950 kPa, about 975 kPa, orabout 1,000 kPa to a high of about 1,025 kPa, about 1,050 kPa, about1,100 kPa, about 1,150 kPa, about 1,200 kPa, about 1,250 kPa, about1,300 kPa, about 1,350 kPa, about 1,400 kPa, about 1,500 kPa, orgreater. In another example, the separator 140 and/or the adsorbent maybe configured to separate the non-hydrocarbons (e.g., CO₂ and/or water)at a pressure from about 600 kPa to about 1,500 kPa, about 650 kPa toabout 1,400 kPa, about 700 kPa to about 1,350 kPa, about 750 kPa toabout 1,300 kPa, about 800 kPa to about 1,250 kPa, about 850 kPa toabout 1,200 kPa, about 900 kPa to about 1,150 kPa, about 950 kPa toabout 1,100 kPa, about 975 kPa to about 1,050 kPa, or about 1,000 kPa toabout 1,025 kPa. In another example, the separator 140 and/or theadsorbent may be configured to separate the non-hydrocarbons (e.g., CO₂and/or water) at a pressure greater than about 900 kPa, greater thanabout 1,000 kPa, greater than about 1,005 kPa, greater than about 1,010kPa, greater than about 1,015 kPa, greater than about 1,020 kPa, greaterthan about 1,025 kPa, greater than about 1,030 kPa, greater than about1,035 kPa, greater than about 1,040 kPa, greater than about 1,045 kPa,greater than about 1,050 kPa, greater than about 1,100 kPa, greater thanabout 1,150 kPa, greater than about 1,200 kPa, greater than about 1,250kPa, greater than about 1,300 kPa, or greater than about 1,400 kPa.

In at least one embodiment, the separator 140 and/or the adsorbentcontained therein may be configured to separate the non-hydrocarbonsfrom the process stream at a predetermined temperature. For example, theseparator 140 and/or the adsorbent may be configured to separate thenon-hydrocarbons (e.g., CO₂ and/or water) at a temperature from a low ofabout 40° C., about 50° C., about 55° C., or about 60° C. to a high ofabout 70° C., about 75° C., about 80° C., about 90° C., or greater. Inanother example, the separator 140 and/or the adsorbent may beconfigured to separate the non-hydrocarbons (e.g., CO₂ and/or water) ata temperature from about 40° C. to about 90° C., about 50° C. to about80° C., about 55° C. to about 75° C., or about 60° C. to about 70° C. Inanother example, the separator 140 and/or the adsorbent may beconfigured to separate the non-hydrocarbons (e.g., CO₂ and/or water) ata temperature greater than about 50° C., greater than about 55° C.,greater than about 60° C., greater than about 65° C., or greater thanabout 70° C. In another example, the separator 140 and/or the adsorbentmay be configured to separate the non-hydrocarbons (e.g., CO₂ and/orwater) at a temperature less than about 100° C., less than about 95° C.,less than about 90° C., less than about 85° C., less than about 80° C.,less than about 75° C., or less than about 70° C. In an exemplaryembodiment, the separator 140 and/or the adsorbent may be configured toseparate the non-hydrocarbons (e.g., CO₂ and/or water) at a temperatureof about 65.5° C.

In at least one embodiment, the non-hydrocarbons (e.g., CO₂ and/orwater) may be desorbed from the adsorbent by directing or flowing apurge gas through the separator 140 to thereby regenerate the separator140 and/or the adsorbent. As the purge gas flows through the separator140, the non-hydrocarbons (e.g., CO₂ and/or water) may desorb from theadsorbent (e.g., molecular sieve) and combine with the purge gas toprovide a regeneration gas including a mixture of the purge gas and thenon-hydrocarbons. In an exemplary embodiment, the separator 140 and/orthe adsorbent contained therein may be configured to adsorb CO₂ and/orwater from the natural gas in the process stream. Accordingly, directingthe purge gas through the separator 140 may provide a regeneration gasincluding a mixture of the purge gas, CO₂, and/or water. In at least oneembodiment, the regeneration gas containing the mixture of the purgegas, CO₂, and/or water may be utilized as fuel for one or more processesor components of the system 100 to thereby increase the energyefficiency of the system 100. For example, as illustrated in FIG. 1, theregeneration gas from the separator 140 may be directed to the internalcombustion engine 130 of the power generation system 126 via line 278and utilized as fuel (e.g., supplemental fuel) therein.

In at least one embodiment, the cooling assembly 106 may include one ormore heat exchangers (three are shown 142, 144, 146) configured toremove at least a portion of the heat from the process stream flowingtherethrough. The heat exchangers 142, 144, 146 may be or include anydevice capable of at least partially cooling or reducing the temperatureof the process fluid flowing therethrough. Illustrative heat exchangers142, 144, 146 may include, but are not limited to, a direct contact heatexchanger, a cooler, a trim cooler, a mechanical refrigeration unit, orthe like, or any combination thereof.

In at least one embodiment, the heat exchangers 142, 144, 146 may befluidly coupled with and/or in thermal communication with thecompression assembly 104. For example, the heat exchangers 142, 144, 146may be fluidly coupled with one or more of the coolers 132, 134, 136,138, and/or the compressor stages 114, 116, 118, 120 of the compressionassembly 104. As illustrated in FIG. 1, a first heat exchanger 142 maybe fluidly coupled with and disposed downstream from the third cooler136 via line 216 and line 218, and may further be fluidly coupled withand disposed upstream of the fourth compressor stage 120 via line 220.As further illustrated in FIG. 1, a second heat exchanger 144 may befluidly coupled with and disposed downstream from the fourth cooler 138via line 224. A third heat exchanger 146 may be fluidly coupled with anddisposed downstream from the first cooler 132 via lines 204 and 206, andmay further be fluidly coupled with and disposed upstream of the secondcompressor stage 116 via line 208. The third heat exchanger 146 may alsobe fluidly coupled with and disposed upstream of the first compressorstage 114 via line 260. In at least one embodiment, one or more of theheat exchangers 142, 144, 146 may be fluidly coupled with the separator140. For example, as illustrated in FIG. 1, the first heat exchanger 142may be fluidly coupled with and disposed downstream from the separator140 via lines 214 and 218.

In at least one embodiment, one or more of the heat exchangers 142, 144,146 may be fluidly coupled with and/or in thermal communication with achiller 148 of the cooling assembly 106. For example, as illustrated inFIG. 1, the first heat exchanger 142 may be fluidly coupled with thechiller 148 via a cooling line 268 and a return line 270, and the secondheat exchanger 144 may be fluidly coupled with the chiller 148 via acooling line 272 and a return line 274. The chiller 148 may beconfigured to cool a process fluid, such as a refrigerant, and directthe refrigerant to each of the first and second heat exchangers 142, 144via the cooling lines 268, 272. The first and second heat exchangers142, 144 may receive the refrigerant from the chiller 148 via thecooling lines 268, 272, and transfer the heat from the process streamflowing therethrough to the refrigerant to thereby reduce thetemperature of the process stream and/or the natural gas containedtherein. The heated refrigerant may be directed back to the chiller 148via the return lines 270, 274 and subsequently cooled therein. WhileFIG. 1 illustrates the chiller 148 fluidly coupled with the first andsecond heat exchangers 142, 144, it may be appreciated that the chiller148 may also be fluidly coupled with and/or in thermal communicationwith any of the heat exchangers and/or coolers of the system 100, andconfigured to deliver the refrigerant to the heat exchangers and/orcoolers of the system 100. For example, the chiller 148 may be fluidlycoupled with and/or in thermal communication with one or more of thecoolers 132, 134, 136, 138 of the compression assembly 104.

In at least one embodiment, one or more of the heat exchangers 142, 144,146 may not be fluidly coupled with the chiller 148. Accordingly, one ormore of the heat exchangers 142, 144, 146 may not be configured toreceive the refrigerant from the chiller 148 to cool the process streamflowing therethrough. For example, as further described herein, thethird heat exchanger 146 may be configured to receive a recycle stream(i.e., second recycle stream) via line 258 to cool the process streamflowing therethrough.

In at least one embodiment, the chiller 148 may be or include a vaporabsorption chiller or non-mechanical chiller configured to receive andbe driven by heat (e.g., waste heat, solar heat, etc.). Illustrativenon-mechanical chillers may include, but are not limited to, ammoniaabsorption chillers, lithium bromide absorption chillers, and the like.In another embodiment, the chiller 148 may be a vapor compressionchiller or mechanical chiller configured to receive and be driven byelectrical energy. For example, as illustrated in FIG. 1, the chiller148 may be a mechanical chiller operatively coupled with the generator128 of the power generation system 126 via line 276 and configured toreceive and be driven by electrical energy from the generator 128. Themechanical chiller 148 may include a compressor (not shown) and anelectric motor (not shown) operatively coupled with the generator 128and configured to drive the compressor. Accordingly, in an exemplaryembodiment, no heat (e.g., waste heat) may be used to drive or operatethe mechanical chiller 148. In at least one embodiment, utilizing themechanical chiller 148 may provide a relatively higher coefficient ofperformance as compared to the non-mechanical chiller.

In at least one embodiment, the liquefaction assembly 108 may includeone or more heat exchangers (four are shown 150, 152, 154, 156) and oneor more expansion elements (two are shown 158, 160) fluidly coupled withthe one or more of the heat exchangers 150, 152, 154, 156. As furtherdescribed herein, the expansion elements 158, 160 may be configured toreceive one or more portions of the process stream and expand theportions to thereby decrease the temperature and pressure of the processstream and generate one or more refrigeration streams. The refrigerationstreams generated by the expansion elements 158, 160 may be directed toone or more of the heat exchangers 150, 152, 154, 156 fluidly coupledtherewith to cool the process stream flowing therethrough. For example,the heat exchangers 150, 152, 154, 156 may receive the refrigerationstreams and transfer heat from the process streams to the refrigerationstreams to thereby cool the process streams.

As illustrated in FIG. 1, a first heat exchanger 150 of the liquefactionassembly 108 may be fluidly coupled with and disposed downstream fromthe second heat exchanger 144 of the cooling assembly 106 via line 226,and a second heat exchanger 152 of the liquefaction assembly 108 may befluidly coupled with and disposed downstream from the first heatexchanger 150 of the liquefaction assembly 108 via line 228. As furtherillustrated in FIG. 1, a third heat exchanger 154 of the liquefactionassembly 108 may be fluidly coupled with and disposed downstream fromthe second heat exchanger 152 via line 230, and a fourth heat exchanger156 of the liquefaction assembly 108 may be fluidly coupled with anddisposed downstream from the third heat exchanger 154 via line 232. Asfurther illustrated in FIG. 1, the third heat exchanger 154 may also befluidly coupled with and disposed upstream of the second heat exchanger152 via line 244, and the fourth heat exchanger 156 may also be fluidlycoupled with and disposed upstream of the first heat exchanger 150 vialine 256.

As previously discussed, one or more of the expansion elements 158, 160may be fluidly coupled with one or more of the heat exchangers 150, 152,154, 156. For example, as illustrated in FIG. 1, a first expansionelement 158 may be fluidly coupled with and disposed downstream from thesecond heat exchanger 152 via lines 230 and 240. The first expansionelement 158 may also be fluidly coupled with and disposed upstream ofthe third heat exchanger 154 via line 242. As further illustrated inFIG. 1, a second expansion element 160 may be fluidly coupled with anddisposed downstream from the third heat exchanger 154 via lines 232 and252. The second expansion element 160 may also be fluidly coupled withand disposed upstream of the fourth heat exchanger 156 via line 254.

In at least one embodiment, one or more of the expansion elements 158,160 may be or include any device capable of converting a pressure and/orenthalpy drop in the process stream into mechanical energy. Theexpansion elements 158, 160 may also be or include any device capable ofexpanding the process stream to decrease the temperature and thepressure of the process stream flowing therethrough. Illustrativeexpansion elements 158, 160 may include, but are not limited to, aturbine or turbo-expander, a geroler, a gerotor, an expansion valve,such as a Joule-Thomson (JT) valve, or the like, or any combinationthereof.

As illustrated in FIG. 1, the first expansion element 158 may be aturbo-expander configured to receive and expand a portion of the processstream from the second heat exchanger 152 to thereby decrease thetemperature and pressure of the process stream flowing therethrough. Inat least embodiment, the turbo-expander 158 may be configured to convertthe pressure drop of the process stream flowing therethrough tomechanical energy. As further described herein, the mechanical energyprovided or generated by the turbo-expander 158 may be utilized to driveone or more devices (e.g., generator, alternator, pump, compressor,etc.). While FIG. 1 illustrates the turbo-expander 158 fluidly coupledwith and disposed downstream from the second heat exchanger 152, it maybe appreciated that the turbo-expander 158 may be fluidly coupled withand disposed downstream from any of the remaining heat exchangers 150,154, 156 of the liquefaction assembly 108. For example, theturbo-expander 158 may be fluidly coupled with and disposed downstreamfrom the first heat exchanger 150, the third heat exchanger 154, and/orthe fourth heat exchanger 156.

In at least one embodiment, the turbo-expander 158 may be coupled withand configured to drive a power generator (not shown) configured toconvert the mechanical energy from the turbo-expander 158 intoelectrical energy. Illustrative power generators may include, but arenot limited to, a generator, an alternator, a motor, or the like, or anycombination thereof. In at least one embodiment, the electrical energyprovided or generated by the power generator may be utilized to driveone or more devices or components of the system 100 to thereby increasethe efficiency of the system 100. For example, the electrical energyfrom the power generator may be utilized (e.g., as supplemental energy)to drive the electric motor 124 of the compression assembly 104.

In another embodiment, the turbo-expander 158 may be operatively coupledwith and configured to drive a compressor 164. For example, asillustrated in FIG. 1, the turbo-expander 158 may be coupled with thecompressor 164 via a driveshaft 166 and configured to deliver themechanical energy (e.g., rotational energy) to the compressor 164 viathe driveshaft 166. The compressor 164 may be configured to utilize themechanical energy from the turbo-expander 158 to compress the processstream flowing therethrough. In at least one embodiment, the compressor164 may be fluidly coupled with one or more of the heat exchangers 150,152, 154, 156 of the liquefaction assembly 108. For example, asillustrated in FIG. 1, the compressor 164 may be fluidly coupled withand disposed downstream of the second heat exchanger 152 via line 246.In at least one embodiment, the compressor 164 may be configured tocompress the process stream to reduce the amount of energy that may berequired to compress the process stream in the compression assembly 104.For example, the compressor 164 may be fluidly coupled with thecompression assembly 104 and configured to deliver the compressedprocess stream thereto. As illustrated in FIG. 1, the compressor 164 maybe fluidly coupled with the third compressor stage 118 of thecompression assembly 104 via line 248 and configured to deliver thecompressed process stream thereto.

As illustrated in FIG. 1, the second expansion element 160 may be orinclude an expansion valve, such as a JT valve, configured to receiveand expand a portion of the process stream from the third heat exchanger154. The expansion valve 160 may expand the process stream from thethird heat exchanger 154 to thereby decrease the temperature andpressure of the process stream in line 254.

In at least one embodiment, the system 100 may include a storage tank168 fluidly coupled with the liquefaction assembly 108 and configured toreceive and store the natural gas (e.g., the LNG) in the process streamfrom the liquefaction assembly 108. For example, as illustrated in FIG.1, the storage tank 168 may be fluidly coupled with and disposeddownstream from the fourth heat exchanger 156 of the liquefactionassembly 108 via lines 234 and 236 and configured to receive and storethe LNG in the process stream from the fourth heat exchanger 156. Thestorage tank 168 may be or include any container capable of storing thenatural gas (e.g., the LNG and/or the CNG). Illustrative storage tanksmay include, but are not limited to, cryogenic storage tanks, vessels, aDewar-type vessel, or any other container capable of storing the LNGand/or the CNG.

In at least one embodiment, the storage tank 168 may be configured tostore the natural gas at a designed storage pressure. In an exemplaryembodiment, the designed storage pressure of the storage tank 168 may befrom a low of about 100 kPa, about 150 kPa, about 175 kPa, or about 190kPa to a high of about 210 kPa, about 225 kPa, about 250 kPa, about 300kPa, or greater. For example, the designed storage pressure of thestorage tank 168 may be from about 100 kPa to about 300 kPa, about 150kPa to about 250 kPa, about 175 kPa to about 225 kPa, or about 190 kPato about 210 kPa. In at least one embodiment, the storage tank 168 mayhave a maximum storage pressure or a maximum allowable working pressure(MAWP) rating. The MAWP of the storage tank 168 may be greater thanabout 250 kPa, greater than about 300 kPa, greater than about 350 kPa,greater than about 400 kPa, greater than about 500 kPa, or greater thanabout 600 kPa.

In at least one embodiment, a flow control valve or letdown valve 162may be fluidly coupled with and disposed upstream of the storage tank168 and configured to decrease the pressure of the process streamdirected to the storage tank 168. For example, as illustrated in FIG. 1,the letdown valve 162 may be fluidly coupled with line 236 upstream ofthe storage tank 168 and configured to decrease the pressure of theprocess stream flowing therethrough to the designed storage pressure orbelow the MAWP of the storage tank 168. In at least one embodiment, theletdown valve 162 may be configured to decrease the pressure of theprocess stream flowing therethrough while maintaining or substantiallymaintaining the temperature of the process stream flowing therethrough.Accordingly, the process stream in line 236 may have a temperature equalto or substantially equal to the process stream in line 234. In at leastone embodiment, the letdown valve 162 may also be configured to maintaina pressure of the process stream in one or more portions of the system100. For example, the letdown valve 162 may be configured to maintainthe pressure (e.g., backpressure) of the process stream in the system100 upstream thereof.

In an exemplary operation of the system 100, a process stream containingnatural gas may be introduced into the system 100 from the natural gassource 102 via line 202. The process stream may be introduced into line202 at a relatively low pressure (e.g., from about 100 kPa to about 500kPa). For example, the process stream in line 202 may have a pressurefrom a low of about 100 kPa, about 150 kPa, about 200 kPa, about 210kPa, about 220 kPa, about 230 kPa, or about 240 kPa to a high of about250 kPa, about 260 kPa, about 270 kPa, about 280 kPa, about 290 kPa,about 300 kPa, about 350 kPa, about 400 kPa, about 450 kPa, about 500kPa, or greater. In another example the process stream in line 202 mayhave a pressure from about 100 kPa to about 500 kPa, about 150 kPa toabout 450 kPa, about 200 kPa to about 400 kPa, about 200 kPa to about300 kPa, about 210 kPa to about 290 kPa, about 220 kPa to about 280 kPa,about 230 kPa to about 270 kPa, or about 240 kPa to about 260 kPa. Inanother example, the process stream in line 202 may have a pressuregreater than about 200 kPa, greater than about 210 kPa, greater thanabout 220 kPa, greater than about 230 kPa, greater than about 240 kPa,greater than about 250 kPa, greater than about 260 kPa, greater thanabout 300 kPa, greater than about 350 kPa, or greater than about 400kPa. In another example, the process stream in line 202 may have apressure less than about 500 kPa, less than about 450 kPa, less thanabout 400 kPa, less than about 350 kPa, less than about 340 kPa, lessthan about 330 kPa, less than about 320 kPa, less than about 310 kPa,less than about 300 kPa, less than about 290 kPa, less than about 280kPa, less than about 270 kPa, less than about 260 kPa, less than about250 kPa, or less than about 240 kPa. In an exemplary embodiment, theprocess stream in line 202 may have a pressure of about 240 kPa.

In at least one embodiment, the process stream may be introduced intoline 202 at a relatively high temperature (e.g., about 5° C. to about15° C.) or a relatively low temperature (e.g., about 15° C. to about 25°C.). For example, the process stream in line 202 may have a temperaturefrom a low of about 10° C., about 12° C., about 14° C., or about 15° C.to a high of about 16° C., about 18° C., about 20° C., about 22° C., orgreater. In another example, the process stream in line 202 may have atemperature from about 10° C. to about 22° C., about 12° C. to about 20°C., about 14° C. to about 18° C., or about 15° C. to about 16° C. Inanother example, the process stream in line 202 may have a temperaturegreater than about 10° C., greater than about 12° C., greater than about14° C., greater than about 15° C., or greater than about 20° C. Inanother example, the process stream in line 202 may have a temperatureless than about 40° C., less than about 35° C., less than about 20° C.,less than about 18° C., less than about 16° C., less than about 15° C.,less than about 14° C., or less than about 12° C. In an exemplaryembodiment, the process stream in line 202 may have a temperature ofabout 15° C.

In at least one embodiment, a recycle stream (i.e., the second recyclestream) from the first cooler 132 may be combined with the processstream upstream of the separator 140 via line 204 to provide a mixtureof the second recycle stream and the natural gas from the natural gassource 102 in line 206. As further described herein, the second recyclestream in line 204 may include “clean” natural gas. The second recyclestream in line 204 may have a pressure from a low of about 210 kPa,about 220 kPa, about 225 kPa, about 230 kPa, or about 235 kPa to a highof about 245 kPa, about 250 kPa, about 255 kPa, about 260 kPa, about 270kPa, or greater. In another example, the second recycle stream in line204 may have a pressure from about 210 kPa to about 270 kPa, about 220kPa to about 260 kPa, about 225 kPa to about 255 kPa, about 230 kPa toabout 250 kPa, or about 235 kPa to about 245 kPa. In another example,the second recycle stream in line 204 may have a pressure greater thanabout 210 kPa, greater than about 220 kPa, greater than about 225 kPa,greater than about 230 kPa, greater than about 235 kPa, greater thanabout 240 kPa, greater than about 245 kPa, greater than about 250 kPa,greater than about 255 kPa, or greater than about 260 kPa. In anotherexample, the second recycle stream in line 204 may have a pressure lessthan about 280 kPa, less than about 275 kPa, less than about 270 kPa,less than about 265 kPa, less than about 260 kPa, less than about 255kPa, less than about 250 kPa, less than about 245 kPa, less than about240 kPa, less than about 235 kPa, less than about 230 kPa, less thanabout 220 kPa, or less than about 210 kPa. In an exemplary embodiment,the second recycle stream in line 204 may have a pressure substantiallyequal to the pressure of the process stream in line 202. For example,the pressure of the second recycle stream in line 204 may be about 240kPa.

In at least one embodiment, the second recycle stream in line 204 mayhave a temperature from a low of about 20° C., about 25° C., about 30°C., or about 35° C. to a high of about 45° C., about 50° C., about 55°C., about 60° C., or greater. For example, the second recycle stream inline 204 may have a temperature from about 20° C. to about 60° C., about25° C. to about 55° C., about 30° C. to about 50° C., or about 35° C. toabout 45° C. In another example, the second recycle stream in line 204may have a temperature greater than about 25° C., greater than about 30°C., greater than about 35° C., greater than about 38° C., or greaterthan about 40° C. In another example, the second recycle stream in line204 may have a temperature less than about 65° C., less than about 60°C., less than about 55° C., less than about 50° C., less than about 48°C., less than about 46° C., or less than about 44° C. In an exemplaryembodiment, the second recycle stream in line 204 may have a temperatureof about 40.5° C.

As previously discussed, the process stream in line 206 may include amixture of the natural gas from the natural gas source 102 and thesecond recycle stream from the first cooler 132. In an exemplaryembodiment, the second recycle stream in line 204 may be combined withthe process stream in line 202 to increase the temperature of theprocess stream in line 206. For example, the temperature of the processstream in line 206 may be from a low of about 16° C., about 18° C.,about 20° C., or about 22° C. to a high of about 26° C., about 28° C.,about 30° C., about 32° C., or greater. In another example, the processstream in line 206 may have a temperature from about 16° C. to about 32°C., about 18° C. to about 30° C., about 20° C. to about 28° C., or about22° C. to about 26° C. In another example, the process stream in line206 may have a temperature greater than about 16° C., greater than about18° C., greater than about 20° C., greater than about 22° C., or greaterthan about 24° C. In another example, the process stream in line 206 mayhave a temperature less than about 36° C., less than about 34° C., lessthan about 32° C., less than about 30° C., less than about 28° C., lessthan about 26° C., less than about 24° C., or less than about 22° C. Inat least one embodiment, combining the second recycle stream in line 204with the process stream in line 202 may not substantially increase ordecrease the pressure of the process stream in line 206. For example,the pressure of the process stream in line 202 may be substantiallyequal to the pressure of the process stream in line 204. In an exemplaryembodiment, the pressure of the process stream in line 206 may be about240 kPa.

The process stream in line 206, containing the mixture of the secondrecycle stream and the natural gas from the natural gas source 102, maybe directed to the third heat exchanger 146 of the cooling assembly 106.The third heat exchanger 146 may absorb at least a portion of the heatin the process stream in line 206 and direct the process stream to thesecond compressor stage 116 via line 208. The third heat exchanger 146may cool the process stream to a temperature from a low of about 8° C.,about 9° C., about 10° C., or about 11° C. to a high of about 13° C.,about 14° C., about 15° C., about 16° C., or greater. For example, theprocess stream in line 208 may have a temperature from about 8° C. toabout 16° C., about 9° C. to about 15° C., about 10° C. to about 14° C.,or about 11° C. to about 13° C. In another example, the process streamin line 208 may have a temperature greater than about 8° C., greaterthan about 9° C., greater than about 10° C., greater than about 11° C.,or greater than about 12° C. In another example, the process stream inline 208 may have a temperature less than about 18° C., less than about17° C., less than about 16° C., less than about 15° C., less than about14° C., or less than about 13° C. In an exemplary embodiment, theprocess stream in line 208 may have a temperature of about 12° C. In atleast one embodiment, the pressure of the process stream in line 208 maybe substantially equal to the pressure of the process stream in line206. For example, the pressure of the process stream in line 208 may befrom about 220 kPa or about 230 kPa. In an exemplary embodiment, thepressure of the process stream in line 208 may be about 227 kPa.

In at least one embodiment, the second compressor stage 116 may compressthe process stream in line 208 and direct the compressed process streamto line 210. As previously discussed, the separator 140 and/or theadsorbent contained therein may be configured to adsorb thenon-hydrocarbons (e.g., CO2 and/or water) at a predetermined separationpressure. Accordingly, in an exemplary embodiment, the second compressorstage 116 may be configured to compress the process stream to thepredetermined separation pressure of the separator 140.

In at least one embodiment, the second compressor stage 116 may compressthe process stream from line 208 to a pressure from a low of about 1,000kPa, about 1,020 kPa, about 1,030 kPa, about 1,040 kPa, or about 1,050kPa to a high of about 1,060 kPa, about 1,070 kPa, about 1,080 kPa,about 1,090 kPa, about 1,100 kPa, or greater. For example, the pressureof the process stream in line 210 may be from about 1,010 kPa to about1,100 kPa, about 1,020 kPa to about 1,090 kPa, about 1,020 kPa to about1,080 kPa, about 1,030 kPa to about 1,070 kPa, or about 1,040 kPa toabout 1,060 kPa. In another example, the pressure of the process streamin line 210 may be greater than about 1,000 kPa, greater than about1,010 kPa, greater than about 1,020 kPa, greater than about 1,030 kPa,greater than about 1,040 kPa, greater than about 1,050 kPa, or greaterthan about 1,060 kPa. In another example, the pressure of the processstream in line 210 may be less than about 1,200 kPa, less than about1,100 kPa, less than about 1,080 kPa, less than about 1,060 kPa, lessthan about 1,040 kPa, or less than about 1,020 kPa. In an exemplaryembodiment, the pressure of the process stream in line 210 may be about1,055 kPa.

In at least one embodiment, compressing the process stream in the secondcompressor stage 116 may generate heat (e.g., the heat of compression)to thereby increase the temperature of the process stream in line 210.For example, the process stream in line 210 may have a temperature froma low of about 95° C., about 100° C., about 102° C., or about 104° C. toa high of about 106° C., about 108° C., about 110° C., about 115° C., orgreater. In another example, the process stream in line 210 may have atemperature from about 95° C. to about 115° C., about 100° C. to about110° C., about 102° C. to about 108° C., or about 104° C. to about 106°C. In another example, the process stream in line 210 may have atemperature greater than about 100° C., greater than about 102° C.,greater than about 104° C., greater than about 106° C., or greater thanabout 108° C. In another example, the process stream in line 210 mayhave a temperature less than about 110° C., less than about 108° C.,less than about 106° C., less than about 105° C., or less than about104° C. In an exemplary embodiment, the process stream in line 210 mayhave a temperature of about 104° C.

In at least one embodiment, the process stream in line 210 may bedirected to the second cooler 134 of the compression assembly 104. Thesecond cooler 134 may absorb at least a portion of the heat (e.g., theheat of compression) from the process stream and direct the processstream to the separator 140 fluidly coupled therewith via line 212. Inat least one embodiment, the second cooler 134 may cool the processstream from line 210 to a temperature from a low of about 40° C., about50° C., about 55° C., or about 60° C. to a high of about 70° C., about75° C., about 80° C., about 90° C., or greater. For example, the processstream in line 212 may have a temperature from about 40° C. to about 90°C., about 50° C. to about 80° C., about 55° C. to about 75° C., or about60° C. to about 70° C. In another example, the process stream in line212 may have a temperature greater than about 50° C., greater than about55° C., greater than about 60° C., greater than about 65° C., or greaterthan about 70° C. In another example, the process stream in line 212 mayhave a temperature less than about 100° C., less than about 95° C., lessthan about 90° C., less than about 85° C., less than about 80° C., lessthan about 75° C., or less than about 70° C. In an exemplary embodiment,the temperature of the process stream in line 212 may be about 65.5° C.

In at least one embodiment, the pressure of the process stream in line212 may be at the predetermined separation pressure of the separator140. For example, the pressure of the process stream in line 212 may befrom a low of about 600 kPa, about 650 kPa, about 700 kPa, about 750kPa, about 800 kPa, about 850 kPa, about 900 kPa, about 950 kPa, about975 kPa, or about 1,000 kPa to a high of about 1,025 kPa, about 1,050kPa, about 1,100 kPa, about 1,150 kPa, about 1,200 kPa, about 1,250 kPa,about 1,300 kPa, about 1,350 kPa, about 1,400 kPa, about 1,500 kPa, orgreater. In another example, the pressure of the process stream in line212 may be about 600 kPa to about 1,500 kPa, about 650 kPa to about1,400 kPa, about 700 kPa to about 1,350 kPa, about 750 kPa to about1,300 kPa, about 800 kPa to about 1,250 kPa, about 850 kPa to about1,200 kPa, about 900 kPa to about 1,150 kPa, about 950 kPa to about1,100 kPa, about 975 kPa to about 1,050 kPa, or about 1,000 kPa to about1,025 kPa. In another example, the process stream in line 212 may have apressure greater than about 900 kPa, greater than about 1,000 kPa,greater than about 1,005 kPa, greater than about 1,010 kPa, greater thanabout 1,015 kPa, greater than about 1,020 kPa, greater than about 1,025kPa, greater than about 1,030 kPa, greater than about 1,035 kPa, greaterthan about 1,040 kPa, greater than about 1,045 kPa, greater than about1,050 kPa, greater than about 1,100 kPa, greater than about 1,150 kPa,greater than about 1,200 kPa, greater than about 1,250 kPa, greater thanabout 1,300 kPa, or greater than about 1,400 kPa. In an exemplaryembodiment, the pressure of the process stream in line 212 may be about1,027 kPa.

As previously discussed, the separator 140 may receive the processstream via line 212, separate at least a portion of the non-hydrocarbonsfrom the process stream, and direct the process stream to line 214. Inat least one embodiment, the separator 140 may separate water and/or CO₂from the natural gas in the process stream to thereby provide theprocess stream in line 214 with “clean” natural gas. For example, theseparator 140 may remove water and/or CO₂ from the natural gas in theprocess stream to increase the relative concentration of thehydrocarbons and provide the “clean” natural gas. The terms “clean”natural gas or “clean” process stream may refer to any natural gas orprocess stream that has been processed by the separator 140 to remove atleast a portion of the non-hydrocarbons contained therein. The terms“clean” natural gas or “clean” process stream may also refer to anynatural gas or process stream having a concentration of CO₂ from a lowof about 1%, about 2%, about 3%, about 4%, or about 5% to a high ofabout 10%, about 12%, about 14%, about 16%, about 18%, about 20%, orgreater. For example, the “clean” natural gas or the “clean” processstream may have a concentration of CO₂ less than 20%, less than about18%, less than about 15%, less than about 10%, less than about 5%, lessthan about 4%, less than about 2%, or less than about 1%. The terms“clean” natural gas or “clean” process stream may further refer to anynatural gas or process stream having a concentration of water from a lowof about 1%, about 2%, about 3%, about 4%, or about 5% to a high ofabout 10%, about 12%, about 14%, about 16%, about 18%, about 20%, orgreater. For example, the “clean” natural gas or the “clean” processstream may have a concentration of water less than about 20%, less thanabout 18%, less than about 15%, less than about 10%, less than about 5%,less than about 4%, less than about 2%, or less than about 1%.

In at least one embodiment, the process stream in line 214 may have apressure from a low of about 925 kPa, about 935 kPa, about 945 kPa,about 950 kPa, or about 955 kPa to a high of about 960 kPa, about 965kPa, about 970 kPa, about 980 kPa, about 990 kPa, or greater. Forexample, the pressure of the process stream in line 214 may be fromabout 925 kPa to about 990 kPa, about 935 kPa to about 980 kPa, about945 kPa to about 970 kPa, about 950 kPa to about 965 kPa, or about 955kPa to about 960 kPa. In another example, the pressure of the processstream in line 214 may be greater than about 925 kPa, greater than about935 kPa, greater than about 945 kPa, greater than about 950 kPa, greaterthan about 955 kPa, greater than about 960 kPa, greater than about 965kPa, greater than about 970 kPa, or greater than about 980 kPa. Inanother example, the pressure of the process stream in line 214 may beless than about 1,000 kPa, less than about 990 kPa, less than about 980kPa, less than about 970 kPa, less than about 965 kPa, less than about960 kPa, or less than about 955 kPa. In an exemplary embodiment, thepressure of the process stream in line 214 may be about 958 kPa.

In at least one embodiment, the process stream in line 214 may have atemperature from a low of about 40° C., about 45° C., about 50° C., orabout 55° C. to a high of about 65° C., about 70° C., about 75° C.,about 80° C., or greater. For example, the process stream in line 214may have a temperature from about 40° C. to about 80° C., about 45° C.to about 75° C., about 50° C. to about 70° C., or about 55° C. to about65° C. In another example, the process stream in line 214 may have atemperature greater than about 40° C., greater than about 50° C.,greater than about 55° C., greater than about 60° C., or greater thanabout 65° C. In another example, the process stream in line 214 may havea temperature less than about 90° C., less than about 80° C., less thanabout 70° C., less than about 65° C., less than about 60° C., less thanabout 55° C., or less than about 50° C. In an exemplary embodiment, thetemperature of the process stream in line 214 may be about 60° C.

In at least one embodiment, a recycle stream (i.e., the first recyclestream) from the third cooler 136 may be combined with the processstream in line 214 downstream from the separator 140 via line 216. Asfurther described herein, the first recycle stream in line 216 mayinclude “clean” natural gas. The first recycle stream in line 216 mayhave a temperature relatively lower than the temperature of the processstream in line 214. For example, the temperature of the first recyclestream in line 216 may be from a low of about 20° C., about 25° C.,about 30° C., or about 35° C. to a high of about 45° C., about 50° C.,about 55° C., about 60° C., or greater. In another example, the firstrecycle stream in line 216 may have a temperature from about 20° C. toabout 60° C., about 25° C. to about 55° C., about 30° C. to about 50°C., or about 35° C. to about 45° C. In another example, the firstrecycle stream in line 216 may have a temperature greater than about 25°C., greater than about 30° C., greater than about 35° C., greater thanabout 38° C., or greater than about 40° C. In another example, the firstrecycle stream in line 216 may have a temperature less than about 65°C., less than about 60° C., less than about 55° C., less than about 50°C., less than about 48° C., less than about 46° C., less than about 44°C., or less than about 42° C. In an exemplary embodiment, the firstrecycle stream in line 216 may have a temperature of about 40.5° C. Inat least one embodiment, the pressure of the first recycle stream inline 216 may be substantially equal to the pressure of the processstream in line 214. For example, the pressure of the first recyclestream in line 216 may be about 958 kPa.

In at least one embodiment, the process stream in line 218 may include amixture of the natural gas from the natural gas source 102, the firstrecycle stream, and/or the second recycle stream. In an exemplaryembodiment, combining the first recycle stream in line 216 with theprocess stream in line 214 may increase the temperature of the processstream. For example, the temperature of the process stream in line 218may be from a low of about 30° C., about 35° C., about 40° C., about 45°C., or about 50° C. to a high of about 55° C., about 60° C., about 65°C., about 70° C., about 75° C., or greater. In another example, theprocess stream in line 206 may have a temperature from about 30° C. toabout 75° C., about 35° C. to about 70° C., about 40° C. to about 65°C., or about 45° C. to about 60° C. In another example, the processstream in line 218 may have a temperature greater than about 35° C.,greater than about 40° C., greater than about 45° C., greater than about50° C., or greater than about 55° C. In another example, the processstream in line 218 may have a temperature less than about 75° C., lessthan about 70° C., less than about 65° C., less than about 60° C., lessthan about 55° C., or less than about 50° C. As previously discussed,the pressure of the first recycle stream in line 216 may besubstantially equal to the pressure of the process stream in line 214.Accordingly, combining the first recycle stream in line 216 with theprocess stream in line 214 may not substantially increase or decreasethe pressure of the process stream in line 218. In an exemplaryembodiment, the pressure of the process stream in line 218 may be about958 kPa.

In at least one embodiment, the process stream in line 218 may bedirected to the first heat exchanger 142 of the cooling assembly 106 andsubsequently cooled therein. As previously discussed, the first heatexchanger 142 may be fluidly coupled with the chiller 148 and configuredto receive the refrigerant therefrom via the cooling line 268. The firstheat exchanger 142 may transfer the heat from the process stream to therefrigerant to thereby reduce the temperature of the process stream inline 220. For example, the temperature of the process stream in line 220may be from a low of about −10° C., about −5° C., about 0° C., or about1° C. to a high of about 2° C., about 3° C., about 5° C., about 10° C.,or greater. In another example, the process stream in line 220 may havea temperature from about −10° C. to about 10° C., about −5° C. to about5° C., about 0° C. to about 3° C., or about 1° C. to about 2° C. Inanother example, the process stream in line 220 may have a temperaturegreater than about −10° C., greater than about −5° C., greater thanabout −2° C., greater than about 0° C., or greater than about 1° C. Inanother example, the process stream in line 220 may have a temperatureless than about 10° C., less than about 8° C., less than about 6° C.,less than about 4° C., less than about 2° C., less than about 1.5° C.,less than about 1° C., or less than about 0° C. In an exemplaryembodiment, the temperature of the process stream in line 220 may beabout 1.7° C. In at least one embodiment, the pressure of the processstream in line 220 may be equal to or substantially equal to thepressure of the process stream in line 218. For example, the pressure ofthe process stream in line 220 may be from about 940 kPa to about 960kPa. In an exemplary embodiment, the pressure of the process stream maybe from about 945 kPa.

In at least one embodiment, the process stream from the first heatexchanger 142 may be directed to the fourth compressor stage 120 vialine 220. The fourth compressor stage 120 may compress the processstream from line 220 and direct the compressed process stream to line222. The fourth compressor stage 120 may compress the process streamfrom line 220 to a pressure from a low of about 2,630 kPa, about 2,635kPa, about 2,640 kPa, about 2,645 kPa, or about 2,647 kPa to a high ofabout 2,648 kPa, about 2,650 kPa, about 2,655 kPa, about 2,660 kPa,about 2,665 kPa, or greater. For example, the pressure of the processstream in line 222 may be from about 2,630 kPa to about 2,665 kPa, about2,640 kPa to about 2,655 kPa, about 2,645 kPa to about 2,650 kPa, orabout 2,647 kPa to about 2,648 kPa. In another example, the pressure ofthe process stream in line 222 may be greater than about 2,630 kPa,greater than about 2,635 kPa, greater than about 2,640 kPa, greater thanabout 2,645 kPa, greater than about 2,650 kPa, greater than about 2,660kPa, greater than about 2,670 kPa, or greater than about 2,680 kPa. Inanother example, the pressure of the process stream in line 222 may beless than about 2,675 kPa, less than about 2,670 kPa, less than about2,665 kPa, less than about 2,660 kPa, less than about 2,655 kPa, lessthan about 2,650 kPa, or less than about 2,648 kPa. In an exemplaryembodiment, the pressure of the process stream in line 222 may be about2,648 kPa.

In at least one embodiment, compressing the process stream in the fourthcompressor stage 120 may generate heat (e.g., the heat of compression)to thereby increase the temperature of the process stream in line 222.For example, the process stream in line 222 may have a temperature froma low of about 75° C., about 78° C., about 80° C., or about 82° C. to ahigh of about 84° C., about 85° C., about 88° C., about 90° C., orgreater. In another example, the process stream in line 222 may have atemperature from about 75° C. to about 90° C., about 78° C. to about 88°C., about 80° C. to about 85° C., or about 82° C. to about 84° C. Inanother example, the process stream in line 222 may have a temperaturegreater than about 70° C., greater than about 75° C., greater than about78° C., greater than about 80° C., or greater than about 82° C. Inanother example, the process stream in line 222 may have a temperatureless than about 94° C., less than about 92° C., less than about 90° C.,less than about 88° C., less than about 86° C., less than about 84° C.,less than about 82° C., or less than about 80° C. In an exemplaryembodiment, the process stream in line 222 may have a temperature ofabout 83° C.

As illustrated in FIG. 1, the process stream in line 222 may be directedto the fourth cooler 138 of the compression assembly 104. The fourthcooler 138 may absorb at least a portion of the heat (e.g., the heat ofcompression) from the process stream and direct the process stream tothe second heat exchanger 144 of the cooling assembly 106 via line 224.In at least one embodiment, the process stream in line 224 may have atemperature from a low of about 20° C., about 25° C., about 30° C., orabout 35° C. to a high of about 45° C., about 50° C., about 55° C.,about 60° C., or greater. For example, the process stream in line 224may have a temperature from about 20° C. to about 60° C., about 25° C.to about 55° C., about 30° C. to about 50° C., or about 35° C. to about45° C. In another example, the process stream in line 224 may have atemperature greater than about 25° C., greater than about 30° C.,greater than about 35° C., greater than about 38° C., or greater thanabout 40° C. In another example, the process stream in line 224 may havea temperature less than about 65° C., less than about 60° C., less thanabout 55° C., less than about 50° C., less than about 48° C., less thanabout 46° C., less than about 44° C., or less than about 42° C. In anexemplary embodiment, the process stream in line 224 may have atemperature of about 40.5° C. In at least one embodiment, the pressureof the process stream in line 224 may be substantially equal to thepressure of the process stream in line 222. For example, the pressure ofthe process stream in line 224 may be from about 2,620 kPa to about2,650 kPa. In an exemplary embodiment, the pressure of the processstream in line 224 may be about 2,620 kPa.

The second heat exchanger 144 of the cooling assembly 106 may furthercool the process stream from the fourth cooler 138 and direct the cooledprocess stream to line 226. As previously discussed, the second heatexchanger 144 may be fluidly coupled with the chiller 148 and configuredto receive the refrigerant therefrom via the cooling line 272. Thesecond heat exchanger 144 may transfer the heat from the process streamto the refrigerant to thereby reduce the temperature of the processstream in line 226. For example, the temperature of the process streamin line 226 may be from a low of about −30° C., about −25° C., about−22° C., or about −20° C. to a high of about −19° C., about −17° C.,about −15° C., about −10° C., or greater. In another example, theprocess stream in line 226 may have a temperature from about −30° C. toabout −10° C., about −25° C. to about −15° C., about −22° C. to about−17° C., or about −20° C. to about −19° C. In another example, theprocess stream in line 226 may have a temperature greater than about−30° C., greater than about −25° C., greater than about −22° C., greaterthan about −20° C., or greater than about −18° C. In another example,the process stream in line 226 may have a temperature less than about 0°C., less than about −5° C., less than about −10° C., less than about−15° C., less than about −17° C., or less than about −19° C. In anexemplary embodiment, the process stream in line 226 may have atemperature of about −19.5° C.

In at least one embodiment, the pressure of the process stream in line226 may be from a low of about 2,545 kPa, about 2,550 kPa, about 2,555kPa, about 2,560 kPa, or about 2,563 kPa to a high of about 2,568 kPa,about 2,570 kPa, about 2,575 kPa, about 2,580 kPa, about 2,585 kPa, orgreater. For example, the pressure of the process stream in line 226 maybe from about 2,545 kPa to about 2,585 kPa, about 2,550 kPa to about2,580 kPa, about 2,555 kPa to about 2,575 kPa, about 2,560 kPa to about2,570 kPa, or about 2,563 kPa to about 2,568 kPa. In an exemplaryembodiment, the pressure of the process stream in line 226 may be about2,565 kPa.

In at least one embodiment, at least a portion of the process stream inline 226 may contain the natural gas in the supercritical state. Forexample, at least a portion of the process stream in line 226 maycontain the CNG. As illustrated in FIG. 1, the process stream in line226 may be directed to the first heat exchanger 150 of the liquefactionassembly 108 and subsequently cooled therein. In at least oneembodiment, a refrigeration stream (i.e., the second refrigerationstream) may be directed to the first heat exchanger 150 via line 256 tocool the process stream in line 226. As further described herein, thesecond refrigeration stream may be provided by the expansion valve 160of the liquefaction assembly 108. The first heat exchanger 150 maytransfer heat from the process stream to the second refrigeration streamand direct the cooled process stream to the second heat exchanger 152 ofthe liquefaction assembly 108 via line 228. In at least one embodiment,the first heat exchanger 150 may cool the process stream to atemperature from a low of about −40° C., about −38° C., about −33° C.,or about −30° C. to a high of about −28° C., about −25° C., about −20°C., about −15° C., or greater. For example, the process stream in line228 may have a temperature from about −40° C. to about −15° C., about−38° C. to about −20° C., about −33° C. to about −25° C., or about −30°C. to about −28° C. In another example, the process stream in line 228may have a temperature greater than about −40° C., greater than about−38° C., greater than about −33° C., greater than about −30° C., orgreater than about −29° C. In another example, the process stream inline 228 may have a temperature less than about −28° C., less than about−25° C., less than about −20° C., less than about −15° C., or less thanabout −10° C. In an exemplary embodiment, the process stream in line 228may have a temperature of about −29° C. In at least one embodiment, thepressure of the process stream in line 228 may be substantially equal tothe pressure of the process stream in line 226. For example, thepressure of the process stream in line 228 may be from about 2,555 kPato about 2,565 kPa. In an exemplary embodiment, the pressure of theprocess stream in line 228 may be about 2,558 kPa.

In at least one embodiment, the second heat exchanger 152 may absorb atleast a portion of the heat in the process stream and direct at least aportion of the process stream to the third heat exchanger 154 of theliquefaction assembly 108 via line 230. A refrigeration stream (i.e.,the first refrigeration stream) may be directed to the second heatexchanger 152 via line 244 to cool the process stream in line 228. Asfurther described herein, the first refrigeration stream may be providedby the turbo-expander 158 of the liquefaction assembly 108. The secondheat exchanger 152 may transfer heat from the process stream to thefirst refrigeration stream and direct at least a portion of the cooledprocess stream to the third heat exchanger 154 via line 230. As furtherdescribed herein, at least a portion of the cooled process stream fromthe second heat exchanger 152 may also be directed to the turbo-expander158 to generate the first refrigeration stream.

In at least one embodiment, the second heat exchanger 152 may cool theprocess stream to a temperature from a low of about −85° C., about −80°C., about −75° C., or about −70° C. to a high of about −65° C., about−60° C., about −55° C., about −50° C., or greater. For example, theprocess stream in line 230 may have a temperature from about −85° C. toabout −50° C., about −80° C. to about −55° C., about −75° C. to about−60° C., or about −70° C. to about −65° C. In another example, theprocess stream in line 230 may have a temperature greater than about−85° C., greater than about −80° C., greater than about −75° C., greaterthan about −70° C., or greater than about −68° C. In another example,the process stream in line 230 may have a temperature less than about−50° C., less than about −55° C., less than about −60° C., less thanabout −65° C., or less than about −68° C. In an exemplary embodiment,the temperature of the process stream in line 230 may be about 68° C. Inat least one embodiment, the pressure of the process stream in line 230may be substantially equal to the pressure of the process stream in line228. For example, the pressure of the process stream in line 230 may befrom about 2,550 kPa to about 2,560 kPa. In an exemplary embodiment, thepressure of the process stream in line 230 may be about 2,551 kPa.

The third heat exchanger 154 may absorb at least a portion of the heatin the process stream and direct at least a portion of the processstream to the fourth heat exchanger 156 of the liquefaction assembly 108via line 232. In at least one embodiment, a refrigeration stream (i.e.,the first refrigeration stream) may be directed to the third heatexchanger 154 via line 242 to cool the process stream flowingtherethrough. The third heat exchanger 154 may transfer heat from theprocess stream to the first refrigeration stream and direct at least aportion of the cooled process stream to the fourth heat exchanger 156via line 232. As further described herein, at least a portion of thecooled process stream from the third heat exchanger 154 may also bedirected to the expansion valve 160 to generate the second refrigerationstream.

In at least one embodiment, the third heat exchanger 154 may cool theprocess stream to a temperature from a low of about −130° C., about−125° C., about −122° C., or about −120° C. to a high of about −115° C.,about −112° C., about −110° C., about −105° C., or greater. For example,the process stream in line 232 may have a temperature from about −130°C. to about −105° C., about −125° C. to about −110° C., about −122° C.to about −112° C., or about −120° C. to about −115° C. In anotherexample, the process stream in line 232 may have a temperature greaterthan about −130° C., greater than about −125° C., greater than about−120° C., greater than about −115° C., or greater than about −110° C. Inanother example, the process stream in line 232 may have a temperatureless than about −100° C., less than about −105° C., less than about−110° C., less than about −112° C., or less than about −115° C. In anexemplary embodiment, the process stream in line 232 may have atemperature of about −117° C. In at least one embodiment, the pressureof the process stream in line 232 may be substantially equal to thepressure of the process stream in line 230. For example, the pressure ofthe process stream in line 232 may be from about 2,540 kPa to about2,560 kPa. In an exemplary embodiment, the pressure of the processstream in line 232 may be about 2,551 kPa.

In at least one embodiment, at least a portion of the process stream inline 232 may contain the natural gas in the supercritical state and/orthe subcritical state. For example, at least a portion of the processstream in line 232 may contain the CNG and/or the LNG. As previouslydiscussed, at least a portion of the process stream from the third heatexchanger 154 may be directed to the fourth heat exchanger 156 via line232 and cooled therein. In at least one embodiment, the fourth heatexchanger 156 may cool the process stream and/or the natural gascontained therein to the subcritical state. For example, the fourth heatexchanger 156 may be configured to cool the process stream and/or thenatural gas contained therein to a temperature below its saturationtemperature (i.e., boiling point), at a given or predetermined pressure.According, the fourth heat exchanger 156 may be configured to cool atleast a portion of the natural gas in the process stream to LNG. Inanother embodiment, the fourth heat exchanger 156 may be configured tosubcool the process stream and/or the natural gas contained therein.

In at least one embodiment, a refrigeration stream (i.e., the secondrefrigeration stream) may be directed to the fourth heat exchanger 156via line 254 to cool the process stream in line 232. The fourth heatexchanger 156 may transfer heat from the process stream to the secondrefrigeration stream and direct the cooled process stream to the letdownvalve 162 via line 234. In at least one embodiment, the fourth heatexchanger 156 may cool the process stream to a temperature from a low ofabout −175° C., about −170° C., about −165° C., or about −160° C. to ahigh of about −155° C., about −150° C., about −145° C., about −140° C.,or greater. For example, the process stream in line 234 may have atemperature from about −175° C. to about −140° C., about −170° C. toabout −145° C., about −165° C. to about −150° C., or about −160° C. toabout −155° C. In another example, the process stream in line 234 mayhave a temperature greater than about −180° C., greater than about −170°C., greater than about −165° C., greater than about −160° C., or greaterthan about −155° C. In another example, the process stream in line 234may have a temperature less than about −140° C., less than about −145°C., less than about −150° C., less than about −155° C., less than about−150° C., or less than about −145° C. In an exemplary embodiment, theprocess stream in line 234 may have a temperature of about −157° C. Inat least one embodiment, the pressure of the process stream in line 234may be substantially equal to the pressure of the process stream in line232. For example, the pressure of the process stream in line 234 may befrom about 2,530 kPa to about 2,560 kPa. In an exemplary embodiment, thepressure of the process stream in line 234 may be about 2,537 kPa.

In at least one embodiment, the letdown valve 162 may decrease thepressure of the process stream in line 234 and direct the process streamto the storage tank 168 via line 236. The pressure of the process streamin line 236 may be from a low of about 195 kPa, about 200 kPa, about 202kPa, about 205 kPa, or about 206 kPa to a high of about 208 kPa, about210 kPa, about 212 kPa, about 215 kPa, about 225 kPa, or greater. Forexample, the pressure of the process stream in line 236 may be fromabout 195 kPa to about 220 kPa, about 200 kPa to about 215 kPa, about202 kPa to about 212 kPa, about 205 kPa to about 210 kPa, or about 206kPa to about 208 kPa. In another example, the pressure of the processstream in line 236 may be greater than about 196 kPa, greater than about200 kPa, greater than about 202 kPa, greater than about 205 kPa, greaterthan about 206 kPa, greater than about 207 kPa, greater than about 208kPa, or greater than about 210 kPa. In another example, the pressure ofthe process stream in line 236 may be less than about 230 kPa, less thanabout 225 kPa, less than about 220 kPa, less than about 218 kPa, lessthan about 216 kPa, less than about 214 kPa, less than about 212 kPa, orless than about 210 kPa. In an exemplary embodiment, the pressure of theprocess stream in line 236 may be about 207 kPa.

As previously discussed, the letdown valve 162 may be configured todecrease the pressure of the natural gas in the process stream whilemaintaining or substantially maintaining the temperature of the naturalgas in the process stream. Accordingly, the temperature of the processstream in line 236 may be equal or substantially equal to the processstream in line 234. For example, the temperature of the process streamin line 236 may be from a low of about −175° C., about −170° C., about−165° C., or about −160° C. to a high of about −155° C., about −150° C.,about −145° C., about −140° C., or greater. In another example, theprocess stream in line 236 may have a temperature from about −175° C. toabout −140° C., about −170° C. to about −145° C., about −165° C. toabout −150° C., or about −160° C. to about −155° C. In another example,the process stream in line 236 may have a temperature greater than about−180° C., greater than about −170° C., greater than about −165° C.,greater than about −160° C., or greater than about −155° C. In anotherexample, the process stream in line 236 may have a temperature less thanabout −140° C., less than about −145° C., less than about −150° C., lessthan about −155° C., less than about −160° C., or less than about −165°C. In an exemplary embodiment, the temperature of the process stream inline 236 may be about −157° C.

As previously discussed, at least a portion of the process stream fromthe second heat exchanger 152 may be directed to the turbo-expander 158to generate the first refrigeration stream. For example, as illustratedin FIG. 1, a portion of the process stream from the second heatexchanger 152 may be directed to the turbo-expander 158 via line 240 togenerate the first refrigeration stream. The turbo-expander 158 mayexpand the portion of the process stream from the second heat exchanger152 to decrease the temperature and pressure of the process stream andthereby generate the first refrigeration stream in line 242. In at leastone embodiment, the first refrigeration stream in line 242 may have apressure from a low of about 150 kPa, about 155 kPa, about 160 kPa,about 165 kPa, or about 170 kPa to a high of about 175 kPa, about 180kPa, about 185 kPa, about 190 kPa, about 195 kPa, or greater. Forexample, the pressure of the first refrigeration stream in line 242 maybe from about 150 kPa to about 195 kPa, about 155 kPa to about 190 kPa,about 160 kPa to about 185 kPa, about 165 kPa to about 180 kPa, or about170 kPa to about 175 kPa. In another example, the pressure of the firstrefrigeration stream in line 242 may be greater than about 150 kPa,greater than about 155 kPa, greater than about 160 kPa, greater thanabout 165 kPa, greater than about 170 kPa, greater than about 175 kPa,greater than about 180 kPa, or greater than about 185 kPa. In anotherexample, the pressure of the first refrigeration stream in line 242 maybe less than about 200 kPa, less than about 195 kPa, less than about 190kPa, less than about 185 kPa, less than about 180 kPa, less than about175 kPa, less than about 170 kPa, or less than about 165 kPa. In anexemplary embodiment, the pressure of the first refrigeration stream inline 242 may be about 172 kPa.

In at least one embodiment, the first refrigeration stream in line 242may have a temperature from a low of about −160° C., about −155° C.,about −150° C., about −145° C., about −140° C. to a high of about −135°C., about −130° C., about −125° C., about −120° C., about −115° C. orgreater. For example, the first refrigeration stream in line 242 mayhave a temperature from about −160° C. to about −115° C., about −155° C.to about −120° C., about −150° C. to about −125° C., about −145° C. toabout −130° C., or about −140° C. to about −135° C. In another example,the first refrigeration stream in line 242 may have a temperaturegreater than about −160° C., greater than about −155° C., greater thanabout −150° C., greater than about −145° C., or greater than about −140°C. In another example, the first refrigeration stream in line 242 mayhave a temperature less than about −120° C., less than about −125° C.,less than about −130° C., less than about −135° C., or less than about−140° C. In an exemplary embodiment, the first refrigeration stream inline 242 may have a temperature of about −137° C.

In at least one embodiment, the first refrigeration stream in line 242may be directed to one or more of the heat exchangers 150, 152, 154, 156of the liquefaction assembly 108. For example, as illustrated in FIG. 1,the first refrigeration stream may be directed to the third heatexchanger 154 via line 242 to absorb the heat from the process streamflowing therethrough from line 230 to line 232. In at least oneembodiment, the first refrigeration stream may be heated in the thirdheat exchanger 154 to a temperature from a low of about −115° C., about−110° C., about −105° C., or about −100° C. to a high of about −95° C.,about −90° C., about −85° C., about −80° C., or greater. For example,the first refrigeration stream in line 244 may have a temperature fromabout −115° C. to about −80° C., about −110° C. to about −85° C., about−105° C. to about −90° C., or about −100° C. to about −95° C. In anotherexample, the first refrigeration stream in line 244 may have atemperature greater than about −115° C., greater than about −110° C.,greater than about −105° C., greater than about −100° C., or greaterthan about −95° C. In another example, the first refrigeration stream inline 244 may have a temperature less than about −80° C., less than about−85° C., less than about −90° C., less than about −95° C., less thanabout −100° C., or less than about −105° C. In an exemplary embodiment,the first refrigeration stream in line 244 may have a temperature ofabout −98° C.

In at least one embodiment, the pressure of the first refrigerationstream in line 244 may be from a low of about 130 kPa, about 135 kPa,about 140 kPa, about 145 kPa, or about 150 kPa to a high of about 155kPa, about 160 kPa, about 165 kPa, about 170 kPa, about 175 kPa, orgreater. For example, the pressure of the first refrigeration stream inline 244 may be from about 130 kPa to about 175 kPa, about 135 kPa toabout 170 kPa, about 140 kPa to about 165 kPa, about 145 kPa to about160 kPa, or about 150 kPa to about 155 kPa. In another example, thepressure of the first refrigeration stream in line 244 may be greaterthan about 130 kPa, greater than about 135 kPa, greater than about 140kPa, greater than about 145 kPa, greater than about 150 kPa, greaterthan about 155 kPa, greater than about 160 kPa, or greater than about165 kPa. In another example, the pressure of the first refrigerationstream in line 244 may be less than about 180 kPa, less than about 175kPa, less than about 170 kPa, less than about 165 kPa, less than about160 kPa, less than about 155 kPa, less than about 150 kPa, or less thanabout 145 kPa. In an exemplary embodiment, the pressure of the firstrefrigeration stream in line 244 may be about 151 kPa.

In at least one embodiment, the first refrigeration stream from thethird heat exchanger 154 may be directed to the second heat exchanger152 via line 244 to absorb the heat from the process stream flowingtherethrough. The first refrigeration stream may be heated in the secondheat exchanger 152 to a temperature from a low of about −60° C., about−55° C., about −50° C., or about −45° C. to a high of about −40° C.,about −35° C., about −30° C., about −25° C., or greater. For example,the first refrigeration stream in line 246 may have a temperature fromabout −60° C. to about −25° C., about −55° C. to about −30° C., about−50° C. to about −35° C., or about −45° C. to about −40° C. In anotherexample, the first refrigeration stream in line 246 may have atemperature greater than about −60° C., greater than about −55° C.,greater than about −50° C., greater than about −45° C., or greater thanabout −40° C. In another example, the first refrigeration stream in line246 may have a temperature less than about −20° C., less than about −25°C., less than about −30° C., less than about −35° C., or less than about−40° C. In an exemplary embodiment, the first refrigeration stream inline 246 may have a temperature of about −42° C.

In at least one embodiment, the pressure of the first refrigerationstream in line 246 may be from a low of about 95 kPa, about 100 kPa,about 105 kPa, about 110 kPa, or about 115 kPa to a high of about 120kPa, about 125 kPa, about 130 kPa, about 135 kPa, about 140 kPa, orgreater. For example, the pressure of the first refrigeration stream inline 246 may be from about 95 kPa to about 140 kPa, about 100 kPa toabout 135 kPa, about 105 kPa to about 130 kPa, about 110 kPa to about125 kPa, or about 115 kPa to about 120 kPa. In another example, thepressure of the first refrigeration stream in line 246 may be greaterthan about 95 kPa, greater than about 100 kPa, greater than about 105kPa, greater than about 110 kPa, greater than about 115 kPa, greaterthan about 120 kPa, or greater than about 125 kPa. In another example,the pressure of the first refrigeration stream in line 246 may be lessthan about 150 kPa, less than about 145 kPa, less than about 140 kPa,less than about 135 kPa, less than about 130 kPa, less than about 125kPa, or less than about 120 kPa. In an exemplary embodiment, thepressure of the first refrigeration stream in line 246 may be about 117kPa.

In at least one embodiment, the first refrigeration stream in line 246may contain “clean” natural gas, and may be directed to the compressionassembly 104 to provide the first recycle stream for the system 100. Forexample, the first refrigeration stream in line 246 may be directed tothe compression assembly 104 as the first recycle stream andsubsequently combined with the process stream flowing through thecompression assembly 104. In at least one embodiment, the first recyclestream may be compressed before being directed to the compressionassembly 104 via line 248. For example, as illustrated in FIG. 1, thefirst recycle stream may be compressed in the compressor 164 beforebeing directed to the compression assembly 104. In at least oneembodiment, the compressor 164 may compress the first recycle stream toa pressure from a low of about 275 kPa, about 280 kPa, about 285 kPa,about 290 kPa, or about 295 kPa to a high of about 300 kPa, about 305kPa, about 310 kPa, about 315 kPa, about 320 kPa, or greater. Forexample, the pressure of the first recycle stream in line 248 may befrom about 275 kPa to about 320 kPa, about 280 kPa to about 315 kPa,about 285 kPa to about 310 kPa, about 290 kPa to about 305 kPa, or about295 kPa to about 300 kPa. In another example, the pressure of the firstrecycle stream in line 248 may be greater than about 275 kPa, greaterthan about 280 kPa, greater than about 285 kPa, greater than about 290kPa, greater than about 295 kPa, greater than about 300 kPa, greaterthan about 305 kPa, greater than about 310 kPa, or greater than about315 kPa. In another example, the pressure of the first recycle stream inline 248 may be less than about 320 kPa, less than about 315 kPa, lessthan about 310 kPa, less than about 305 kPa, less than about 300 kPa,less than about 295 kPa, or less than about 290 kPa. In an exemplaryembodiment, the pressure of the first recycle stream in line 248 may beabout 297 kPa.

In at least one embodiment, compressing the first recycle stream in thecompressor 164 may generate heat (e.g., the heat of compression) tothereby increase the temperature of the first recycle stream in line248. For example, the first recycle stream in line 248 may have atemperature from a low of about 2° C., about 3° C., about 4° C., orabout 5° C. to a high of about 7° C., about 8° C., about 9° C., about10° C., or greater. In another example, the first recycle stream in line248 may have a temperature from about 2° C. to about 10° C., about 3° C.to about 9° C., about 4° C. to about 8° C., or about 5° C. to about 7°C. In another example, the first recycle stream in line 248 may have atemperature greater than about 0° C., greater than about 1° C., greaterthan about 2° C., greater than about 3° C., or greater than about 4° C.In another example, the first recycle stream in line 248 may have atemperature less than about 10° C., less than about 9° C., less thanabout 8° C., less than about 7° C., less than about 6° C., or less thanabout 5° C. In an exemplary embodiment, the first recycle stream in line248 may have a temperature of about 6° C.

In at least one embodiment, the compressor 164 may be configured tocompress the first recycle stream to a selected inlet pressure of one ormore compressor stages 114, 116, 118, 120 of the compression assembly104. For example, as illustrated in FIG. 1, the compressor 164 may befluidly coupled with the third compressor stage 118 via line 248 andconfigured to compress the first recycle stream to the selected inletpressure of the third compressor stage 118. In at least one embodiment,the selected inlet pressure of the compressor stages 114, 116, 118, 120may be determined by the operating parameters of the compressor 112. Thethird compressor stage 118 may compress the first recycle stream fromline 248 and direct the compressed first recycle stream to the thirdcooler 136 via line 250. The first recycle stream may be cooled in thethird cooler 136 and subsequently combined with the process stream inline 214 via line 216, as discussed above.

In at least one embodiment, the third compressor stage 118 may compressthe first recycle stream to a pressure from a low of about 940 kPa,about 945 kPa, about 950 kPa, about 955 kPa, or about 960 kPa to a highof about 970 kPa, about 979 kPa, about 980 kPa, about 985 kPa, about 990kPa, or greater. For example, the pressure of the first recycle streamin line 250 may be from about 940 kPa to about 990 kPa, about 945 kPa toabout 985 kPa, about 950 kPa to about 980 kPa, about 955 kPa to about975 kPa, or about 960 kPa to about 970 kPa. In another example, thepressure of the first recycle stream in line 250 may be greater thanabout 940 kPa, greater than about 950 kPa, greater than about 955 kPa,greater than about 960 kPa, or greater than about 965 kPa. In anotherexample, the pressure of the first recycle stream in line 250 may beless than about 1,000 kPa, less than about 995 kPa, less than about 990kPa, less than about 985 kPa, less than about 980 kPa, less than about975 kPa, or less than about 970 kPa. In an exemplary embodiment, thepressure of the first recycle stream in line 250 may be about 965 kPa.

In at least one embodiment, compressing the first recycle stream in thethird compressor stage 118 may generate heat (e.g., the heat ofcompression) to thereby increase the temperature of the first recyclestream in line 250. For example, the first recycle stream in line 250may have a temperature from a low of about 65° C., about 70° C., about75° C., or about 80° C. to a high of about 85° C., about 90° C., about95° C., about 100° C., or greater. In another example, the first recyclestream in line 250 may have a temperature from about 65° C. to about100° C., about 70° C. to about 95° C., about 75° C. to about 90° C., orabout 80° C. to about 85° C. In another example, the first recyclestream in line 250 may have a temperature greater than about 65° C.,greater than about 70° C., greater than about 75° C., greater than about80° C., or greater than about 85° C. In another example, the firstrecycle stream in line 250 may have a temperature less than about 105°C., less than about 100° C., less than about 95° C., less than about 90°C., or less than about 85° C. In an exemplary embodiment, the firstrecycle stream in line 250 may have a temperature of about 83° C.

As previously discussed, at least a portion of the process stream fromthe third heat exchanger 154 may be directed to the expansion valve 160to generate the second refrigeration stream. For example, as illustratedin FIG. 1, a portion of the process stream from the third heat exchanger154 may be directed to the expansion valve 160 via line 252 to generatethe second refrigeration stream. The expansion valve 160 may expand theportion of the process stream from the third heat exchanger 154 todecrease the temperature and pressure of the process stream and therebygenerate the second refrigeration stream in line 254. In at least oneembodiment, expanding the portion of the process stream through theexpansion valve 160 may flash the process stream into a two-phase fluidincluding a vapor phase and a liquid phase. Accordingly, the secondrefrigeration stream in line 254 may include a liquid phase (e.g., about70% or more) and a vapor phase (e.g., about 30% or less).

In at least one embodiment, the second refrigeration stream in line 254may have a temperature from a low of about −175° C., about −170° C.,about −165° C., or about −160° C. to a high of about −155° C., about−150° C., about −145° C., about −140° C., or greater. For example, thesecond refrigeration stream in line 254 may have a temperature fromabout −175° C. to about −140° C., about −170° C. to about −145° C.,about −165° C. to about −150° C., or about −160° C. to about −155° C. Inanother example, the second refrigeration stream in line 254 may have atemperature greater than about −175° C., greater than about −170° C.,greater than about −165° C., greater than about −160° C., or greaterthan about −155° C. In another example, the second refrigeration streamin line 254 may have a temperature less than about −130° C., less thanabout −135° C., less than about −140° C., less than about −145° C., lessthan about −150° C., or less than about −155° C. In an exemplaryembodiment, the second refrigeration stream in line 254 may have atemperature of about −158° C.

In at least one embodiment, the second refrigeration stream in line 254may have a pressure from a low of about 10 kPa, about 12 kPa, about 14kPa, about 16 kPa, or about 18 kPa to a high of about 22 kPa, about 24kPa, about 26 kPa, about 28 kPa, about 30 kPa, or greater. In anotherexample, the pressure of the second refrigeration stream in line 254 maybe from about 10 kPa to about 30 kPa, about 12 kPa to about 28 kPa,about 14 kPa to about 26 kPa, about 16 kPa to about 24 kPa, or about 18kPa to about 22 kPa. In another example, the pressure of the secondrefrigeration stream in line 254 may be greater than about 10 kPa,greater than about 12 kPa, greater than about 14 kPa, greater than about16 kPa, greater than about 18 kPa, greater than about 20 kPa, or greaterthan about 22 kPa. In another example, the pressure of the secondrefrigeration stream in line 254 may be less than about 32 kPa, lessthan about 30 kPa, less than about 28 kPa, less than about 26 kPa, lessthan about 24 kPa, or less than about 22 kPa. In an exemplaryembodiment, the pressure of the second refrigeration stream in line 254may be about 20 kPa.

In at least one embodiment, the second refrigeration stream may bedirected to any one or more of the heat exchangers 150, 152, 154, 156 ofthe liquefaction assembly 108 to cool the process fluid flowingtherethrough. For example, as previously discussed, the secondrefrigeration stream may be directed to the fourth heat exchanger 156via line 254 to cool the process stream flowing therethrough. Aspreviously discussed, the second refrigeration stream may sufficientlycool the process stream flowing through the fourth heat exchanger 156 tothe subcritical state to thereby produce the LNG.

In at least one embodiment, cooling the process stream in the fourthheat exchanger 156 may not increase or substantially increase thetemperature of the second refrigeration stream flowing therethrough. Forexample, as previously discussed, the second refrigeration stream inline 254 may be a two-phase fluid including the liquid phase and thevapor phase, and the heat or thermal energy absorbed by the secondrefrigeration stream may serve to vaporize the liquid phase.Accordingly, the liquid portion of the second refrigeration stream inline 254 may prevent or substantially prevent the heat absorbed from theprocess stream from reducing the temperature of the second refrigerationstream flowing through the fourth heat exchanger 156. As such, thesecond refrigeration stream in line 256 may have a temperature equal toor substantially equal to the second refrigeration stream in line 254.For example, the second refrigeration stream in line 256 may have atemperature from a low of about −175° C., about −170° C., about −165°C., or about −160° C. to a high of about −155° C., about −150° C., about−145° C., about −140° C., or greater. In another example, the secondrefrigeration stream in line 256 may have a temperature from about −175°C. to about −140° C., about −170° C. to about −145° C., about −165° C.to about −150° C., or about −160° C. to about −155° C. In anotherexample, the second refrigeration stream in line 256 may have atemperature greater than about −175° C., greater than about −170° C.,greater than about −165° C., greater than about −160° C., or greaterthan about −155° C. In another example, the second refrigeration streamin line 256 may have a temperature less than about −130° C., less thanabout −135° C., less than about −140° C., less than about −145° C., lessthan about −150° C., or less than about −155° C. In an exemplaryembodiment, the second refrigeration stream in line 256 may have atemperature of about −158° C.

In at least one embodiment, the pressure of the second refrigerationstream in line 256 may also be substantially equal to the pressure ofthe second refrigeration stream in line 254. For example the secondrefrigeration stream in line 256 may have a pressure from a low of about10 kPa, about 12 kPa, about 14 kPa, about 16 kPa, or about 18 kPa to ahigh of about 22 kPa, about 24 kPa, about 26 kPa, about 28 kPa, about 30kPa, or greater. In another example, the pressure of the secondrefrigeration stream in line 256 may be from about 10 kPa to about 30kPa, about 12 kPa to about 28 kPa, about 14 kPa to about 26 kPa, about16 kPa to about 24 kPa, or about 18 kPa to about 22 kPa. In anotherexample, the pressure of the second refrigeration stream in line 256 maybe greater than about 10 kPa, greater than about 12 kPa, greater thanabout 14 kPa, greater than about 16 kPa, greater than about 18 kPa,greater than about 20 kPa, or greater than about 22 kPa. In anotherexample, the pressure of the second refrigeration stream in line 256 maybe less than about 32 kPa, less than about 30 kPa, less than about 28kPa, less than about 26 kPa, less than about 24 kPa, or less than about22 kPa. In an exemplary embodiment, the pressure of the secondrefrigeration stream in line 256 may be about 17 kPa.

In at least one embodiment, the second refrigeration stream from thefourth heat exchanger 156 may provide additional cooling to one or moreof the remaining heat exchangers 150, 152, 154. For example, asillustrated in FIG. 1, the second refrigeration stream from the fourthheat exchanger 156 may be directed to the first heat exchanger 150 vialine 256 to cool the process stream flowing therethrough. In at leastone embodiment, the second refrigeration stream may be heated in thefirst heat exchanger 150 to a temperature from a low of about −45° C.,about −40° C., about −35° C., or about −30° C. to a high of about −25°C., about −20° C., about −15° C., about −10° C., or greater. Forexample, the second refrigeration stream in line 258 may have atemperature from about −45° C. to about −10° C., about −40° C. to about−15° C., about −35° C. to about −20° C., or about −30° C. to about −25°C. In another example, the second refrigeration stream in line 258 mayhave a temperature greater than about −45° C., greater than about −40°C., greater than about −35° C., greater than about −30° C., or greaterthan about −25° C. In another example, the second refrigeration streamin line 258 may have a temperature less than about −5° C., less thanabout −10° C., less than about −15° C., less than about −20° C., or lessthan about −25° C. In an exemplary embodiment, the second refrigerationstream in line 258 may have a temperature of about −27° C.

In at least one embodiment, the pressure of the second refrigerationstream in line 258 may be substantially equal to the pressure of thesecond refrigeration stream in line 256. For example, the secondrefrigeration stream in line 258 may have a pressure from a low of about4 kPa, about 6 kPa, about 8 kPa, about 10 kPa, or about 12 kPa to a highof about 16 kPa, about 18 kPa, about 20 kPa, about 22 kPa, about 24 kPa,or greater. In another example, the pressure of the second refrigerationstream in line 258 may be from about 4 kPa to about 24 kPa, about 6 kPato about 22 kPa, about 8 kPa to about 20 kPa, about 10 kPa to about 18kPa, or about 12 kPa to about 16 kPa. In another example, the pressureof the second refrigeration stream in line 258 may be greater than about4 kPa, greater than about 6 kPa, greater than about 8 kPa, greater thanabout 10 kPa, greater than about 12 kPa, greater than about 14 kPa, orgreater than about 16 kPa. In another example, the pressure of thesecond refrigeration stream in line 258 may be less than about 26 kPa,less than about 24 kPa, less than about 22 kPa, less than about 20 kPa,less than about 18 kPa, or less than about 16 kPa. In an exemplaryembodiment, the pressure of the second refrigeration stream in line 258may be about 14 kPa.

In at least one embodiment, the second refrigeration stream in line 258may contain “clean” natural gas, and may be directed to the compressionassembly 104 to provide the second recycle stream for the system 100.For example, the second refrigeration stream in line 258 may be directedto the compression assembly 104 as the second recycle stream andsubsequently combined with the process stream flowing through thecompression assembly 104. In at least one embodiment, the second recyclestream may be directed to one or more of the heat exchangers 142, 144,146 of the cooling assembly 106 before being directed to the compressionassembly 104. For example, as illustrated in FIG. 1, the second recyclestream may be directed to the third heat exchanger 146 of the coolingassembly 106 via line 258 to cool the process stream flowingtherethrough. In at least one embodiment, cooling the process streamflowing through the third heat exchanger 146 with the second recyclestream may increase the efficiency of the compressor 112 and/or thecompression assembly 104. For example, cooling the process stream mayincrease the density of the natural gas in the process stream andthereby decrease the energy or work that may be required to compress theprocess stream in the compressor 112. In at least one embodiment, thesecond recycle stream may cool the process stream in the third heatexchanger 146 to a temperature above the freezing point of water and/orCO₂ to thereby prevent the crystallization of the water and/or the CO₂contained in the process stream.

In at least one embodiment, the third heat exchanger 146 may heat thesecond recycle stream to a temperature from a low of about 2° C., about4° C., about 6° C., or about 8° C. to a high of about 10° C., about 12°C., about 14° C., about 16° C., or greater. For example, the secondrecycle stream in line 260 may have a temperature from about 2° C. toabout 16° C., about 4° C. to about 14° C., about 6° C. to about 12° C.,or about 8° C. to about 10° C. In another example, the second recyclestream in line 260 may have a temperature greater than about 0° C.,greater than about 2° C., greater than about 4° C., greater than about6° C., or greater than about 8° C. In another example, the secondrecycle stream in line 260 may have a temperature less than about 20°C., less than about 18° C., less than about 16° C., less than about 14°C., less than about 12° C., or less than about 10° C. In an exemplaryembodiment, the second recycle stream in line 260 may have a temperatureof about 9° C. In at least one embodiment, the second recycle stream inline 260 may have a pressure equal to or substantially equal to thepressure of the process stream in line 258. For example, the pressure ofthe second recycle stream in line 260 may be from about 4 kPa to about24 kPa. In an exemplary embodiment, the pressure of the second recyclestream in line 260 may be about 7 kPa.

As illustrated in FIG. 1, the first compressor stage 114 may compressthe second recycle stream from line 260 and direct the compressed secondrecycle stream to the first cooler 132 via line 262. In at least oneembodiment, the first compressor stage 114 may compress the secondrecycle stream to a pressure from a low of about 210 kPa, about 220 kPa,about 225 kPa, about 230 kPa, or about 235 kPa to a high of about 245kPa, about 250 kPa, about 255 kPa, about 260 kPa, about 270 kPa, orgreater. For example, the pressure of the second recycle stream in line262 may be from about 210 kPa to about 270 kPa, about 220 kPa to about260 kPa, about 225 kPa to about 255 kPa, about 230 kPa to about 250 kPa,or about 235 kPa to about 245 kPa. In another example, the pressure ofthe second recycle stream in line 262 may be greater than about 210 kPa,greater than about 220 kPa, greater than about 225 kPa, greater thanabout 230 kPa, greater than about 235 kPa, greater than about 240 kPa,greater than about 245 kPa, greater than about 250 kPa, greater thanabout 255 kPa, or greater than about 260 kPa. In another example, thepressure of the second recycle stream in line 262 may be less than about280 kPa, less than about 275 kPa, less than about 270 kPa, less thanabout 265 kPa, less than about 260 kPa, less than about 255 kPa, lessthan about 250 kPa, less than about 245 kPa, less than about 240 kPa,less than about 235 kPa, less than about 230 kPa, less than about 220kPa, or less than about 210 kPa. In an exemplary embodiment, thepressure of the second recycle stream in line 262 may be about 240 kPa.

In at least one embodiment, compressing the second recycle stream in thefirst compressor stage 114 may generate heat (e.g., the heat ofcompression) to thereby increase the temperature of the second recyclestream in line 262. For example, the second recycle stream in line 262may have a temperature from a low of about 75° C., about 80° C., about85° C., or about 90° C. to a high of about 95° C., about 100° C., about105° C., about 110° C., or greater. In another example, the secondrecycle stream in line 262 may have a temperature from about 75° C. toabout 110° C., about 80° C. to about 105° C., about 85° C. to about 100°C., or about 90° C. to about 95° C. In another example, the secondrecycle stream in line 262 may have a temperature greater than about 75°C., greater than about 80° C., greater than about 85° C., greater thanabout 90° C., or greater than about 100° C. In another example, thesecond recycle stream in line 262 may have a temperature less than about120° C., less than about 115° C., less than about 110° C., less thanabout 105° C., less than about 100° C., or less than about 95° C. In anexemplary embodiment, the second recycle stream in line 262 may have atemperature of about 93° C.

As illustrated in FIG. 1, the second recycle stream in line 262 may becooled in the first cooler 132 and subsequently combined with theprocess stream in line 202 upstream of the separator 140 via line 204,as discussed above. In at least one embodiment, combining the secondrecycle stream with the process stream upstream of the separator 140 mayreduce the amount of non-hydrocarbons (e.g., water and/or CO₂) to beremoved by the separator 140. For example, at least a portion of thesecond recycle stream in line 204 may contain natural gas that has been“cleaned” in the separator 140, or “clean” natural gas, and the processstream in line 202, upstream of the separator 140, may contain naturalgas from the natural gas source 102 that may not have been “cleaned” inthe separator 140. As such, the second recycle stream in line 204 mayhave a relatively lower concentration of water and/or CO₂ than theprocess stream in line 202. Accordingly, combining the second recyclestream in line 204 with the process stream in line 202 may decrease theconcentration of the non-hydrocarbons in the process stream directed tothe separator 140 and thereby reduce the amount of water and/or CO₂ tobe removed by the separator 140. In at least one embodiment, reducingthe amount of water and/or CO₂ to be removed by the separator 140 maydecrease the frequency of regenerating the separator 140 and/or theadsorbent contained therein.

In at least one embodiment, the first refrigeration stream may not becombined or mixed with the second refrigeration stream in theliquefaction assembly 108 and/or one or more components thereof. Forexample, the first refrigeration stream and the second refrigerationstream may be directed to separate and distinct heat exchangers 150,152, 154, 156 of the liquefaction assembly 108. As illustrated in FIG.1, the first refrigeration stream from the turbo-expander 158 may bedirected to the second and third heat exchangers 152, 154, and thesecond refrigeration stream from the expansion valve 160 may be directedto the first and fourth heat exchangers 150, 156.

FIG. 2 illustrates a flowchart of a method 300 for producing liquefiednatural gas, according to one or more embodiments. The method 300 mayinclude compressing a process stream containing natural gas from anatural gas source in a compression assembly fluidly coupled with thenatural gas source to produce a compressed process stream, as shown at302. The method 300 may also include removing one or morenon-hydrocarbons from the compressed process stream in a separatorfluidly coupled with the compression assembly, as shown at 304. Themethod 300 may further include cooling the compressed process streamwith a cooling assembly fluidly coupled with the compression assembly tothereby produce a cooled, compressed process stream containing thenatural gas in a supercritical state, as shown at 306. The method 300may also include expanding a first portion of the natural gas in thecooled, compressed process stream in a first expansion element togenerate a first refrigeration stream, as shown at 308. The method 300may also include expanding a second portion of the natural gas in thecooled, compressed process stream in a second expansion element togenerate a second refrigeration stream, as shown at 310. The method 300may also include cooling at least a portion of the natural gas in thecooled, compressed process stream to a subcritical state with the firstrefrigeration stream and the second refrigeration stream to therebyproduce the liquefied natural gas, as shown at 312.

FIG. 3 illustrates a flowchart of another method 400 for producingliquefied natural gas, according to one or more embodiments. The method400 may include compressing natural gas from a natural gas source in acompression assembly fluidly coupled with the natural gas source, asshown at 402. The method 400 may also include removing water and carbondioxide from the natural gas in a separator fluidly coupled with thecompression assembly, as shown at 404. The method 400 may furtherinclude cooling the natural gas to supercritical natural gas with amechanical chiller configured to receive and be driven by electricalenergy, as shown at 406. The method 400 may also include expanding afirst portion of the supercritical natural gas in a first expansionelement to generate a first refrigeration stream, as shown at 408. Themethod 400 may also include expanding a second portion of thesupercritical natural gas in a second expansion element to generate asecond refrigeration stream, as shown at 410. The method 400 may alsoinclude cooling the remaining supercritical natural gas to subcriticalnatural gas with the first refrigeration stream and the secondrefrigeration stream to thereby produce the liquefied natural gas, asshown at 412.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the present disclosure. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions, and alterations hereinwithout departing from the spirit and scope of the present disclosure.

We claim:
 1. A method for producing liquefied natural gas, comprising: compressing a process stream containing natural gas from a natural gas source in a compression assembly fluidly coupled with the natural gas source to product a compressed process stream; removing one or more non-hydrocarbons from the compressed process stream in a separator fluidly coupled with the compression assembly; cooling the compressed process stream with a cooling assembly fluidly coupled with the compression assembly, thereby producing a cooled, compressed process stream containing the natural gas in a supercritical state; expanding a first portion of the natural gas in the cooled, compressed process stream in a first expansion element to generate a first refrigeration stream; expanding a second portion of the natural gas in the cooled, compressed process stream in a second expansion element to generate a second refrigeration stream; cooling at least a portion of the natural gas in the cooled, compressed process stream to a subcritical state with the first refrigeration stream and the second stream, thereby producing the liquefied natural gas; feeding the first refrigeration stream to the compression assembly as a first recycle stream; and combining the compressed first recycle stream with the compressed process stream downstream from the separator; feeding the second refrigeration stream to the compression assembly as a second recycle stream; and combining the compressed second recycle stream with the process stream upstream of the separator.
 2. The method of claim 1, wherein the second expansion element is an expansion valve.
 3. The method of claim 1, wherein the first expansion element is a turbo-expander.
 4. The method of claim 3, further comprising: expanding the first portion of the cooled, compressed process stream in the turbo-expander to generate mechanical energy; and driving a compressor coupled with the turbo-expander with the mechanical energy to compress the first recycle stream.
 5. The method of claim 1, wherein cooling the at least a portion of the natural gas in the cooled, compressed process stream to the subcritical state with the first refrigeration stream and the second refrigeration stream comprises: cooling the at least a portion of the natural gas in the cooled, compressed process stream in a first heat exchanger with the first refrigeration stream; and cooling the at least a portion of the natural gas in the cooled, compressed process stream in a second heat exchanger with the second refrigeration stream.
 6. The method of claim 1, wherein the cooling assembly includes a mechanical chiller configured to receive and be driven by electrical energy.
 7. The method of claim 1, wherein compressing the process stream in the compression assembly comprises: generating heat from the compression of the process stream; and absorbing at least a portion of the heat generated from the compression of the process stream with a cooler of the compression assembly.
 8. The method of claim 1, wherein removing the one or more non-hydrocarbons from the compressed process stream in the separator comprises removing water and carbon dioxide from the natural gas in the separator at a pressure greater than about 1,000 kPa.
 9. A method for producing liquefied natural gas, comprising: compressing natural gas from a natural gas source in a compression assembly fluidly coupled with the natural gas source; removing water and carbon dioxide from the natural gas in a separator fluidly coupled with the compression assembly; cooling the natural gas to supercritical natural gas with a mechanical chiller configured to receive and be drive by electrical energy; expanding a first portion of the supercritical natural gas in a first expansion element to generate a first refrigeration stream; expanding a second portion of the supercritical natural gas in a second expansion element to generate a second refrigeration stream; and cooling the remaining supercritical natural gas to subcritical natural gas with the first refrigeration stream and the second refrigeration stream, thereby producing the liquefied natural gas; feeding the first refrigeration stream to the compression assembly as a first recycle stream; combining the compressed first recycle stream with the natural gas downstream from the separator; feeding the second refrigeration stream to the compression assembly as a second recycle stream; and combining the compressed second recycle stream with the natural gas upstream of the separator.
 10. The method of claim 9, wherein the first expansion element is a turbo-expander, and the second expansion element is an expansion valve.
 11. The method of claim 9, further comprising removing water and carbon dioxide from the natural gas in the separator at a pressure greater than about 1,000 kPa.
 12. The method of claim 9, further comprising: combusting a portion of the natural gas from the natural gas source in an internal combustion engine to produce mechanical energy; generating the electrical energy in a generator operatively coupled with the internal combustion engine; and directing at least a portion of the electrical energy to the mechanical chiller.
 13. The method of claim 9, wherein cooling the remaining supercritical natural gas to the subcritical natural gas with the first refrigeration stream and the second refrigeration stream comprises: cooling the remaining supercritical natural gas with the first refrigeration stream in a first heat exchanger; and cooling the remaining supercritical natural gas with the second refrigeration stream in a second heat exchanger. 